I think that the fpr isn't necessarily worthless, but a stocker would be close enough usually, just depends. My car likes higher f/p, so it was benificial to me, and normally I would recommend one to play around with for tuning. As far as the exhaust leak, I don't know how bad one would affect you, but I had 3 cylinders with leaks, and when I tightened them back up, I felt a good amt of power coming back. I would try to tighten up that header bolt, and check the rest to be sure, and like stated previously, chk vacuum leaks, codes, timing, f/p, ect..