Those performers are not going to do you any favors on top end. Trickflow twisted wedges are where its at, they are incredible. I have 3 friends with 5.0 stangs. One is mostly stock with a cam, one has a 306 with TF heads, cam and intake, the otherone is ford racing heads, cam and intake with a 306 also. The TF is QUITE a bit faster than the ford racing car, and if I'm not mistaken, the gt40 heads perform about the same as the performers.