The new 3.5-liter V6 takes the RX beyond snappy to a feeling of real power without sacrificing the trademark smoothness. Indeed, this V6 is so powerful that it responds aggressively, even abruptly, to anything more than a bit of gas. It takes a bit of practice to adjust to the throttle response.

Lexus can no longer claim that its hybrid RX 400h accelerates more quickly that the conventional gasoline V6. The RX 350 squirts from 0 to 60 mph in 7.3 seconds, or 7.4 seconds with all-wheel drive. It's a tick quicker than the 400h, and quicker than some V8-powered SUVs.

The five-speed automatic helps exploit the extra power from the RX 350's engine. It quickly kicks down a gear or two when the driver dips the accelerator, and holds that gear all the way to the redline when the pedal is floored, before shifting up smoothly and smartly. With more gears than a traditional four-speed automatic, the five-speed keeps the engine purring in the fat part of the power band. A low first gear offers quicker response off the line, useful when you need to merge into traffic from a standing start. Fifth gear, meanwhile, provides lower engine speeds when cruising, which translates into less engine noise and better gas mileage.

Driving the RX 400h isn't a lot different than driving the RX 350. It's smooth and responsive, yet there are some obvious distinctions that are apparent from the moment it starts up.

Twist the key in the 400h. Everything on the dash lights up, but there's no sound of an engine starting, only silence. Slide the transmission lever to drive and you can pull silently away on electric power. This is not at all intuitive at first because we're all accustomed to hearing and feeling an engine running before shifting into drive. Shifting into drive without sound or vibration can feel strange. You get used to it, though, and we enjoy running in electric-only mode.

At low speeds, the RX 400h is perfectly content to operate in electric-only mode. It's quiet, and you begin to hear things that are normally drowned out by an engine. We found this interesting and enjoyable. It will run in this silent mode in stop-and-go commuter traffic, eliminating the noise and pollution that the cars around you are putting out. The RX 400h maneuvers silently through crowded parking lots as well, where pedestrians often will not hear you coming and therefore won't always get out of the way. You learn to be patient and need to exercise extra care. Toyota's hybrid system is an electric motor assisted by a gas engine, while some of the other hybrid systems are oriented around a gasoline engine assisted by an electric motor.

The V6 engine starts whenever it's needed to supplement the electric motor. Step hard on the gas pedal and the V6 will usually kick in quickly and seamlessly. In all cases the response is immediate acceleration, and plenty of it. The 400h is impressively quick, particularly when overtaking a slower vehicle between 30 and 60 mph.

The RX 400h enjoys a 60-percent edge in fuel efficiency over the RX 350 in the EPA's City cycle, earning 32/27 mpg City/Highway with front-wheel drive. That might look odd at first, as we rarely see EPA ratings with City mileage that exceeds Highway by any amount, much less five miles per gallon. With the RX 400h, it's because the vehicle can run strictly on electric power at lower city speeds, using energy generated in several ways (including the gas engine) and stored in its batteries. The front-drive 400h's EPA combined rating of 29 mpg is comparable to that of the average compact sedan. The average for SUVs in this class is about 16 mpg.

Impressive numbers, to be sure, but we should probably lay one myth to rest right here. The RX 400h will not save its owner a substantial amount of money, compared to an RX 350, in reduced fuel bills. Depending on driving habits, it won't likely pay off before the fifth year of ownership. The RX 350 is an impressively efficient vehicle in its own right, and we've done the math. With a model re-alignment this year, the RX 350 and 400h are equipped identically, so the price difference is strictly for the hybrid powertrain and not extra features such as leather seats or a moonroof. The difference for all-wheel drive models is $3,780. At 15,000 miles per year with gas at $3 per gallon, it will take the 400h driver four years, eight months to recover extra cash spent at purchase, using the EPA's City ratings for both. The cheaper that gas, the longer it takes to recover the initial investment.

Likewise, the more highway driving an owner does, the longer it takes to recover the up-front cost. If a driver achieves something like the EPA combined rating for both cars (it's 22 mpg for the RX 350), which is a more realistic measure of what the typical owner can expect, it takes nine years to recover the extra cost for the RX 400h. That's nearly twice as long as the typical period of ownership. There are plenty of good reasons to buy an RX 400h, not the least of which is reduced environmental impact. Lower cost of ownership is not one of them.

On the downside, the RX 400h drones under light throttle. The sound it makes under acceleration is not entirely pleasing, either. In some test vehicles we could feel the gas V6 kick on and off, and it's a lurch you won't feel in other Lexus products. Also, there's a little torque steer, or at least something that feels similar to torque steer: Pull up to a stop sign, stand on the gas and make a right turn, and you'll feel a slight tug on the steering wheel or a resistance to turning.

The brakes may be the most un-Lexus-like component of the RX 400h. They stop the car with authority, no worries there. But they sometimes feel uneven, as the regenerative effect of the electric motors helped slow the car, which makes it more challenging to modulate the pedal for smooth stops, particularly at parking lot speeds.

No issue at all in the RX 350. Its brakes are smooth and respond with good pedal feel in all circumstances. Its brakes are relatively large and the anti-lock braking system is well tuned, helping a driver maintain steering control during emergency stops. The system features Electronic Brake-force Distribution, which directs braking effort in proportion to weight bias and brake loading for improved stability under hard braking, and Brake Assist, which is designed to sense panic braking and to maintain full braking pressure, even if the driver makes the common mistake of relaxing pressure on the brake pedal.

While it may be the perception that green does not mean fun, the opposite may be true with the RX. The 400h might handle a bit more responsively than the standard RX 350 without the Performance Package, and it certainly feels sportier. The 400h suspension is firmer, and it corners with less lean. Its optional 18-inch wheels come with speed-rated tires that are aggressively sticky.

All RX variants are nearly immune to road noise, even with the large greenhouse and expansive glass, and there's very little wind noise. Lexus engineers took the time to aerodynamically shape the roof rack for quieter running.

The all-wheel-drive systemon models so equipped automatically routes power to the wheels with the best grip and works with the ABS to slow any wheel that slips and spins. The RX 350 is not a serious off-road vehicle, as it has no under-body armor, low-range or locking differentials. Yet if you tread lightly, it's fine for unpaved roads. An RX 400h driver should stick to pavement, or risk damaging the hybrid drivetrain, however. But with all-wheel drive either vehicle is great for the Snow Belt. Deep snow or packed snow (with the right tires) and slippery surfaces are no problem. The RX finds whatever grip is available and adds an element of confidence in bad weather.

The optional Performance Package for the RX 350 features an air suspension with four driver-selectable settings. The air suspension automatically lowers the vehicle by 0.3 inches at speeds higher than 62 mph, to reduce drag for better handling and fuel economy. Drivers can select a mode that lowers the car by 0.6 inches for better cornering and a smoother ride. Rough roads and unpaved trails requiring greater ground clearance can be accommodated by the High position, which raises the ride height by 1.2 inches at speeds up to 30 mph. An Access mode lowers the RX 330 for easier entry and exit when in Park. The Access mode can be programmed to lower the RX automatically when the ignition is turned off, a nice feature.

What's new for 2007: The 3.5-liter V6 in the RX 350 increases horsepower 25 percent to 270 hp over the previous RX 330, and torque by 13 to 251 pound-feet, yet also increases EPA fuel economy rating by 1 mpg. This aluminum V6 features the latest control technology, including Lexus's Variable Valve Timing with Intelligence system (VVT-i), which balances high-rev horsepower with good torque at all engine speeds and low emissions. Also new for 2007 is the front-wheel-drive version of the hybrid-powered RX 400h. The front-wheel-drive version features a single electric motor in front, as opposed to one motor front and one rear on the all-wheel-drive model.