RE: 55AX mid throttle issues, fixed I think
If you run the .75 AX so that its peak RPM on the ground when properly leaned is in the 11,000's, you'll be doing well. However, the 10K-plus range will work......and then whatever prop turns that RPM and flies the airplane well is the one to use.
We'll even turn the .91 at just under 12K for best performance.
O.S. selects props that give the best noise profile coupled with respectable throttle handling. The high "paractical" RPM range, though, tells us that you can really use a higher RPM as a baseline if you're willing or able to handle the increased noise output.