A few weeks ago, and not for the first time, I was involved in a conversation about low-CO2 cars which turned to the question of whether people buy them for green issues or because they cost less to run. As is generally the case, supporters of each side of the argument expressed their opinions stoutly and were not easily persuaded to move to the other.Nobody involved struck me as being the kind of person who might be in the market for an Infiniti, and to judge by the reaction to the introduction of Nissan's luxury brand to Europe this year it seems clear that, if they had, they would not have been involved in the argument at all.The possibly surprising fact is that the most popular Infiniti so far is the FX50S, which is not only the most expensive model the company builds but also the least economical, and the one with the worst CO2 emissions.Whether UK buyers will follow the trend remains to be seen (at the time of writing the brand has been in the UK for less than a month and there is only one dealership, in Reading, though the total should reach 13 within two years) but on the basis that it might it seems appropriate to make the FX50S the first Infiniti to go through our road test process.A word of explanation if you're not up to speed with Infiniti. The FX is the brand's large SUV - quoted rivals include the BMW X6, Porsche Cayenne and Range Rover Sport - and two of the three versions use a 3.7-litre V6 petrol engine (more or less the same as the one in the Nissan 370Z, though not as powerful) and seven-speed automatic transmission.The FX50S has the same gearbox but a five-litre V8 engine producing 385bhp and giving a spritely 0-62mph time of 5.8 seconds. Combined fuel economy is 21.6mpg, and CO2 emissions of 307g/km put the car well into the highest VED bracket.Apart from all that, there are good and bad points. Foremost among the former is the formidable level of equipment. There is no way of being brief about this, so settle down because the rest of this paragraph is going to be a bumpy ride.For your £53,800 you get, among other things, 21" alloy wheels, sports front seats (8-way adjustable for the passenger, 14-way for the driver), very subtle active rear steering, a tyre pressure monitoring system, self-repairing paint, front and rear parking sensors, four-camera around-view monitoring, speed-sensitive power steering, intelligent cruise control, intelligent Brake Assist, and the Connectiviti+ package which consists of an 11-speaker Bose audio system, an excellent 8" colour display, DVD playback, a 10GB Music Box storage system capable of storing 300 CDs' worth of files, DVD playback, voice control and 30GB hard-disk navigation with route recalculation in the event of traffic problems, automatic warning of speed and red-light cameras and Michelin Guides points of interest and restaurant/hotel information.All of this, and more, is standard. There are hardly any options, and they are limited to colour and trim choices.In some ways, though, the FX50S does not feel like it should cost that much. It's hardly the most elegant vehicle on the road (not that many other luxury SUVs are elegant either, but none of them looks quite so much like a cartoon lizard as this one), and although the 5.0 V8 engine is amazingly quiet as well as giving stirring performance, there's quite a lot of wind noise from the front end at motorway cruising speeds, while the road noise is already annoying at 20mph and becomes spectacularly worse the faster you go.The road noise situation probably isn't helped by the low-profile tyres on those 21" wheels, but if they were an extra-cost option to replace more sensible ones people would most likely go for them anyway. The tyres don't help ride quality in the slightest either, though the suspension has been so well set-up that the effect isn't as bad as it might be. For the same reason, the handling is extraordinarily good for a car of this type, and it's hard to get into trouble even when you're using the power liberally.One more thing about the tyres: there isn't a spare. Infiniti has instead gone down the route of supplying a repair kit for use if you get a puncture, but as with all these things it's not going to help if the wheel breaks or the tyre is irreparably damaged by whatever caused the puncture.The only benefit is that the lack of a spare frees up luggage space, of which there is anything from 410 litres to 1305 litres depending on what you do with the seats.The parking sensors and the around-view monitoring system (with the display cleverly arranged on the screen so that you seem to have a single view from a camera mounted well above the roof) are both very useful, and in fact vital given that Infiniti's claim that the FX50S offers "superb all-round visibility" is utter nonsense.Nissan's slapdash approach to visibility, particularly at the rear, has been carried over to its luxury brand, and there is something sadly familiar about the useless little triangular rear side windows, which are almost completely shrouded by trim around the nearest pillar.If I gave you a peashooter and challenged you to hit either of these while sitting in the driver's seat, you'd be doing well to succeed once in every ten attempts. Infiniti would no doubt retort that the camera system overcomes this problem sufficiently, but I don't think it does.There is a lot to admire here, but I feel that in many ways the design could have been much better. Nissan doesn't need to achieve very high sales figures - it has its own-brand models for those - so the FX50S is likely to remain rare, and I suspect that this exclusivity will turn out to be a greater selling point than the actual quality of the car. Engine 5026 cc, 8 cylinders Power 390 bhp @6500 rpm Torque 369 ib/ft @4400 rpm Transmission 7 speed semi-auto Fuel/CO2 21.6 mpg / 307 g/km Acceleration 0-62mph: 5.8sec Top speed 155 mph Price From £53811.00 approx Release date 01/09/2009