I have heard only great things about SPEC, I had a centerforce last time and it was pretty good but I think ill give SPEC a chance next time, I have heard some people havent been too happy with their centerforce dual frictions.
ive had a king cobra at 290hp and it worked fine, didn't slip or anything.
i have a spec stage 3, 6 puck disc right now and it works well. grabs hard during shifts. its not the funnest to drive in traffic though and if you dont get the RPM's right, it will shake your whole car when you let it out slowly lol.