curious, but which ones would be inaccurate?
I am going by what I see at work...
Transmission does not cost 25-30k like you said.
Quick google search.
http://www.conceptzperformance.com/Cart/description.php?II=2765&Car_Type=NISGTR
Mainatence is just like any other car. Beat the crap out of it and will need more mainatence. Your comparing a 60k mustang to 90-100k GTR. Yes parts cost more and so did the initial investment to buy the car.
GTR will beat GT500 off the line stock for stock. Might even edge it out in the 1/4 mile stock for stock. Modified it's any body's game.