The Mag 15 does vary a bit from engine to engine. I have 4 of them for my A class planes, and I try to keep track of which is which, since some pull harder than others. Maybe it's just me and the way I treat my engines though. Anyway, I'd say just let it break in, and see if, in fact, you get to the point were you have to worry about it. I doubt even the best of them will hit over 17.5 on 5%.

fwiw, I was hitting 17.3ish last weekend, on 15% Omega.

Oh, it seems the blue props spin up lower than the black ones, btw.

Hmmm, I wonder if the rules could be adjusted to allow "restricter plates" to be put over the carbs of hot engines to tone them down to the proper RPM limits. Should be easy to do, and we could get rid of all the engine rules except the rpm limit.