To my knowledge, I am stock. I pulled top end all day. And also, I can take traction control off, on dry pavement, and hit 70 mph before i hook up, swear to God. I daily drive a 1994 Z28 Camaro fully built with Lloyd Elliot heads/cam/intake/exhaust/stalled auto/etc. It will run a 12.1 on street tires and dynos in at 375hp. I have more troubles hooking up in this GTP than I do in my camaro.
I think their top end is great. In the couple times that I have raced this GTP, I have had a ridiculous amount of wheelspin off of the line, and only won the races because of the topend.