I use it, it's my right foot. haha Most of us around here are power junkies aned really have to much power. Autocross is the only place where I feel it's a negative. I'm used to my cars power and can modulate the throttle pretty well. I raced my BMW 550i with the traction control on and off. I couldn't stand it with the traction control active. I personally like to feel the car and make my own inputs. That's racing for me. I rode with a guy and his Nissan GTR out at a local SCCA event. We got done and I told him he was a cheater. Traction control and ABS saved his butt at least a couple times. I ended up beating him by a couple seconds.

To finally answer your question, 650hp is PLENTY. I have 666hp and gobs of torque and it's stressing the chassis to the max. I went from a big block making 593hp/587flb's to 666hp/641hp in the same chassis. I could mat the throttle in first gear before and it would dead hook on clean pavement. Now it will make smoke. LOL The same went for autocross. I really could put all the power down. Now I can easily spin the tires as the power comes on. I really think somewhere around 500rwhp is ideal and managable for these chassis. Although I will say that the extra power is nice for the road course.