I have a reactor with a 46ax and it is a good flying plane. As for a 75 being to much I can't anwser. I thought I would tell ya my expereance with the 55 in a sundowner. Mine was always dead sticking on me because it was running hot. I am now almost at 3 and a half turns out from closed on the high end. Mine is very reliable now. Not saying that is your problem but these engines don't do well in closed cowls.

And I am running a OS F plug! An idea that I read on here from someone!