It is almost beyond belief. This car has a 4.3-litre V8 engine under the bonnet, so you know that just a few inches from your toes metal components are thrashing up and down and round about, whipped into action by the explosions of volatile liquid. You may also know that an engine with eight cylinders is inherently less well-balanced than an engine with six. So why, unless you bury the throttle pedal and release every last drop of potential, can you neither hear nor feel the power unit of the GS 430?Because Lexus is, and always has been, the master at suppressing engine noise, that's why. The GS - whether in this form or as the three-litre GS 300 - is described as a "luxury sports saloon", and as far as decibel containment goes it certainly qualifies as a luxury car. This is the equal best thing about the Lexus GS 430.The other equal best thing about the Lexus GS 430 is the fact that it is extraordinarily well-equipped. £46,755 may seem like quite a high price, but it's all you will have to pay because there are no options. After all, for what else could you opt? The 430 has a specification still higher than that of the uppermost GS 300, the SE-L (whose letters may be assumed to stand for Special Equipment - Luxury).The 300 SE-L and the 430 are the only GS models with 18" alloy wheels (rather than 17") and a Mark Levinson 14-speaker audio system (as opposed to a 10-speaker one). Adaptive cruise control with Pre-Crash safety is optional on the SE-L but standard on the GS 430. Vehicle Dynamics Integrated Management and wood trim on the multifunction steering wheel are unique to the 430. No two ways about it - this is a particularly high-specification car.It's all going very well so far. But let's take another look at that "luxury sports saloon" tag. To me, it suggests - among other things - that the GS 430 must be a pleasure to sit in, and I don't think it is. Instead of looking after me, this car seems to be trying to intimidate me. There's a lot of room, but a great deal of it is taken up by heavily scuplted chunks of dashboard and a particularly wide centre console. It's as if these items are trying to squeeze me back out of the cabin where I came from.They certainly do a good job of squeezing out some of the minor controls. Quite a number of these, including the mirror adjustment, headlamp washers and fuel filler cap release button, are hidden away in a compartment to the right of the steering wheel. To use any of them, you have to open the compartment, perform the required function and then - if you don't want your knee to jar against it - close the compartment again, thereby doing three jobs when in other cars you would have had to do just one. Not very user-friendly.To add to the claustrophobic effect of the interior, the shapes of the windows suggest that the top of the car is crowding in on me. Wherever I sit, but especially in the back, I feel more cramped than I actually am. Surely I should not be feeling this way in a luxury car?Or rather, as I was almost forgetting, a luxury sports saloon. How are we doing with that? In terms of the major controls, we're doing very nicely thanks. The steering - speed-sensitive, electrically-controlled - is wonderful to use: creamy, seamless, generally just lovely. And although the six-speed automatic transmission doesn't quite manage to change from one ratio to the other unnoticeably, it's still very refined. Luxury points are being clawed back.And sports points? The GS 430 feels quick, even though it's not devastatingly powerful. 279bhp from 4.3 litres isn't very dramatic these days, and it's interesting to note just how much harder the GS 300 works, with 245bhp from three litres. On the other hand, the 430 is a great deal torquier and produces its maximum power at a significantly lower engine speed. You don't have to work nearly as hard to get the same performance.That's one reason why it feels quick. The other reason is a little more unfortunate: neither the ride nor the handling is up to scratch, and although the Lexus feels terrific through the streets, its progress over anything but perfect out-of-town roads is laboured. On tricky country roads - where you would expect that something described as a sports saloon would be entertaining to drive - you quickly reach the point where the power of the engine overcomes the behaviour of the chassis. At speeds above 30mph the GS 430 is behaves in a way that suggests neither sportiness nor luxury.You can enjoy the GS430 for its level of specification and for its almost miraculous refinement. In other respects it lags behind the best of the opposition. Engine 4293cc, 8 cylinders Power 279bhp Fuel/CO2 24.8mpg / 269g/km Acceleration 0-62mph: 6.1 seconds Top speed 155mph Price £46,755 Details correct at publication date