Of the three powertrains fitted to Infiniti's M saloon, that of the M35h is the most complex. "h" stands for "hybrid", from which you'll gather that there are two power sources, one an electric motor and the other a 3.5-litre V6 petrol engine, which share duties as appropriate depending on whether the driver seems to be looking for performance or fuel economy.The M35h offers rather a lot of both. According to the official figures, it's the most economical M by a substantial margin, with a 40.9mpg combined figure which comfortably beats the 37.7mpg of the M30d diesel. CO2 emissions are the lowest in the range at 159g/km, making the hybrid £85 a year cheaper to tax than the diesel is.It's also the quickest in the range in a straight line. All Infiniti Ms are restricted to a 155mph top speed, but only this one can accelerate from 0-62mph in under six seconds. Curiously, though, it's available only in the GT trim level, which in Infiniti terms is the luxury one. The diesel and the M37 petrol can also be specified in S specification, which is sportier, but this one - quicker than either of those - can't.To be more specific, the test car was a GT Premium, and therefore fitted with intelligent cruise control, forward collision warning, lane departure warning and prevention, blind spot warning and intervention, an "eco pedal" (which resists heavy-footedness in the interests of better fuel economy), nicely smelly Forest Air climate control air-conditioning, a 30GB hard-disk satellite navigation system and a 16-speaker Bose surround-sound audio system, all of which adds £3970 to the price of a regular GT.Accordingly, this car is a direct equivalent of the M30d GT Premium reviewed a couple of years ago, and since many of the comments made there also apply here I'll leave you to make with the clickage rather than repeat them here.I would, however, quite like to mention once more the view out of the windscreen, which is greatly enhanced by the swooping front wings. A luxury car this may be, but those wings give it quite a sense of purpose. It's as if the car is saying, "My priority is to get you where you want to go in as much comfort as possible, but I will also do this very quickly if that's what you want."Despite that, the M35h doesn't feel quite as rapid as another hybrid from a Japanese brand trying to hide the mainstream origins of the parent company, namely the Lexus GS 450h. On paper the Lexus is slower, but it feels more urgent, and it handles a good deal more sportily (ride quality is impressive in both cases).It's also more economical, at least officially, and cheaper to tax. Against that, the Infiniti is, on average across the range, cheaper to buy, as well as being, in my opinion anyway, much better-looking.Given the choice of these very similar cars, I'd have the Lexus. Your mileage, as the saying goes, may vary. Engine 3498cc, 6 cylinders plus electric motor Power 302bhp Transmission 7-speed automatic Fuel/CO2 40.9mpg / 159g/km Acceleration 0-62mph: 5.5 seconds Top speed 155mph Price £45,995 Details correct at publication date