550 horses show up when u smoke a Jag or a Viper from the traffic stop ... and such luxury super cars are for ultra rich who enjoy the power and the comfort, and not to indulge in drag racing. Similarly you will not find an XKR on the race track.
In any case, almost all luxury cars in 2003 and beyond will be crossing 400 hp easily. I will give u the stats from home, but VW Phaeton, Mercs Maybach, Audi A8 and RS6, all are going to be much more powerful than current crop of 350hp commonly found in Lexus LS, Merc S, Q45 and other such cars.
Do you know that most dealerships offer a 3 day, full refund on Viper? Cz they don't allow test drives and many times within 3 days the drivers bring the car back because they can't seem to control the ferocious power of a Viper. One time, I drove it, and completely smoked a Boxster S within secs from zero.