I ran the performer plus in my original 289, I already had the intake,carb and headers prior, I did some mild porting on the ex side of the heads and I was not very impressed at all, seem like maybe 10-15hp from the cam swap. I later swapped that eng into a friends 68FB and we put in the comp 268h and it was tons stronger and no loss in bottm end.
Ok, now where as ide like to have as much as possible, 10-15hp for a part that cost $147 (jegs), isnt too shabby where i come from. Escpecially when the car only weighs in at 2800lbs or so. Thats a pretty good bang for the buck in my book. Well, i just may look into maybe a 260H cam. Ive heard the 268H in a 289 and its too lopey for me.