Great review of the GTR (I'm a rabid Top Gear fan so yes, I'm biased ) Beat the Z06 but a couple of seconds on their track anyway. Sick car.
http://videos.streetfire.net/video/Top-Gear-Nissan-GTR-track_172987.htm
Buuuut, if you just want to go in a straight line, you need the 400 kph (253 mph!) Bugatti Veyron. Speed junkies, you owe it to yourself to watch this video):
http://www.youtube.com/watch?v=jk1t6S737Cs&feature=fvst
forget the Veyron, the Ultimate aero tt beats it by a mile in top speed.