This is not a view that Jaguar would necessarily endorse (and indeed some of the top brass reacted unenthusiastically when I mentioned it recently), but I still feel that the XJ is the car the company most wants to make - perhaps not in financial or marketing terms, but at least to the extent that it is home territory.Although I like all the current XJs, and although if I were to buy one myself it would probably not be the XJR, this 400bhp 4.2-litre supercharged model is without doubt the most dramatic in the range. To me, it has all the usual Jaguar attributes of (in the words of the old advertising slogan) grace, space and pace. I like the shape, even though others complain about its reference to a car first launched in the 1960s; it's very roomy, though there isn't a long-wheelbase version for lanky rear seat passengers; and oh boy, is it quick.It is surprising, though not paradigm-shiftingly so, that a car of this size can leap from 0-62mph in just over five seconds and perform similar high-speed tricks on its way to a limited maximum speed of 155mph. More important is the way it does all this.For example, it does it very quietly. You still hear the muffled roar of the V8 engine when you're using lots of throttle, but compared with previous supercharged Jaguars the none too pleasant whine of the Eaton compressor has been quelled. The original sound effect - something like a greatly extended quack, if you can imagine that - has been reduced to a more distant high-pitched tone which now seems to be part of the engine noise rather than an irritating addition to it.The way you can use the power is also deeply impressive. Regular readers will know that there's an enthusiasm in this office for cars whose suspension set-up includes relatively soft springs controlled by carefully tuned dampers. Several high-performance cars on the market are disappointing because the balance is wrong, and a remarkable proportion suffer disastrously from the exactly opposite condition of over-hard springs mated to dampers that are too weak to control them.The correct arrangement is said to have been achieved for the first time by Mercedes-Benz in 1936, the year that Anglo-German Rudolf Uhlenhaut joined the Grand Prix team as an engineer. "He showed the way to an entirely new era in racing car design," said his boss, Team Manager Alfred Neubauer. "He sprung softly - and damped strongly."Jaguar has done exactly this with the XJR, and the result is a positive score on both sides of the ride/handling balance sheet. This is often referred to as a compromise, but cars like this show that by improving one you can improve the other.So: the XJR has an astonishingly compliant ride - barely more fidgety than that of any other XJ - with no excess roll to cause discomfort to passengers. The same general softness and the same lack of uncontrolled body lean also allow the car to cope with 400bhp being shoved through the rear wheels as if this were the smallest of trifles. It can't actually be true that an upgrade to 500bhp could sensibly be achieved without any reworking of the chassis, but it feels like it.With all this in its favour, the XJR is on the one hand an accomplished cruiser along motorways or through fast, flowing bends, yet it also deals superbly with tight, narrow and perhaps bumpy corners. Like the best of all large, sporting cars, it seems to shrink to the required size on roads which are absorbed into the contours of interesting and challenging scenery.Could it be better? Of course it could. The J-gate selection for the automatic transmission, though better than it used to be, still isn't great. Jaguar knows exactly what to do about this: fit the steering wheel paddle controls that have been introduced to the new-generation XK. For cruising purposes they make no difference at all, but when the going gets tough they provide the XK with a decisive advantage. It will be a great day for enthusiasts of large high-performance saloons if they are ever transferred to the XJR. Engine 4196cc, 8 cylinders Power 400bhp Transmission 5-speed automatic Fuel/CO2 23.0mpg / 299g/km Acceleration 0-62mph: 5.3 seconds Top speed 155mph Price £59,540 Details correct at publication date