Combine that with the fact that each new GTR tested by a magazine seem to be slower than the previous GTR's tested as the cars get closer to an actual production car.
Then again, a 2 car comparason isn't excactly fair. The GTR appears that it will sell for a bit less than a Corvette Z06, with ball park peformance (lastest test shows 0 to 60mph in 4.1 seconds for GTR, 3.8 seconds for the Z06, both numbers could be faster but it's a relative comparason).
It's difficult to know if active suspension will allow a 3800 pound car to peform on a track similar to the ZR1 (3400 lbs), or the lighter still Z06 (3150lbs). However the Ford GT, at 3500lbs, is close to the weight of a GTR, and it's 550hp is enough help it keep up with the Z06.
The best normal looking track car is the Koenigsegg CCX, 806hp, 2600lbs. The fastest street legal track car is probably the Radical SR8, but it's missing stuff that most cars have, like a roof, doors, ... However, the Radical SR8's will spend a lot of time on tracks, while the CCX will just spend time collecting dust between cleanings.