Dave's words don't make this ASP sound very good.

An engine this size, which is supposed to be an OS clone, should not exhibit any over-compression issues, if the 'original' OS .91 wasn't.

As Jim wrote, anything smaller than a 14x6 (13x8, 15x4, 12x10...) is too small.

Most people flying Tai-Ji and similar planes here, with MVVS (and some other) .91 engines, with tuned pipes, use a 14x8 APC and get in the vicinity of 10,000 RPM. Overheating and detonation are not an issue, even for those using 10% nitro.