I am glad you started this thread as I am considering the same project with some other engines. The MAC pretuned for the 61 FX seems an easy way to go as you do not have to R&D the tuning of the pipe. I would call at talk to both JETT and MAC before I made the decision and possibly buy both if I could afford them and do my own independent comparison and then I would know which one performed the best. Just because one gives better numbers on the ground doesn't mean it will perform better in the air. I have a .61 FX and wait your decision and results.