Capt Lou, I have a pair of 125's, one in Rare Bear and the other in a 1/5 scale WACO, (as they are side mount they have the appropriate Slimline mufflers to keep all but the exhaust tubes within the round cowls). Both are strong but I think the design lends more to lower speed torque than RPM. My only advice is to provide adequate mount damping as they can shake a lot of airframe if bolted to a metal or extremely rigid mount.
With a few Saitos in the fleet now my other comment would be that, to me at least, their prop specs always seem a bit on the aggressive side. I would not recommend working with the largest or highest pitch in the range, (and expect to see your higher RPM, as well). This is especially true if working with 3-blade props. On the 91 and 100 I find the best performance with a 13/8 three blade MA. This is at the very bottom of their range for the 91 and below that for the 100. For my scale type of flying those work best.
p.s. I also think you may not be completely worn in yet, even with a gallon and a half out the exhaust. Personally I lean towards that being a good thing. Any engine that peaks early makes me wonder how durable it will prove to be in service.
Last edited by Cougar429; 10-25-2014 at 06:28 PM.