Hello Chris,
Just stating what I oberved, I simply fitted what my supplier termed a sealed bearing, because he didn't have my normal shielded bearing in stock. Using the props that we normally do in stunt, I doubt if there would be much of a difference in observable rpm. I would agree with you if we were talking high rpm engines, but a big prop in the 8000rpm region, well I doubt it and I certainly didn't see much variation, maybe if I had used a tacho?
Regards,
Andrew.