Hi!
I have flown my GP GEE BEE R-2 for 10 times with a MVVS 15cc twostroke engine and performance is rather good,seems to be as good as the Great Planes video with large loops and knife idefinite knife-edge capability.
But I do recommend every one considering this airplane to build it light and not to put a too large (heavy) engine in it.
My weights a little under 5kg and start and flying is easy ...but landings are a bit demanding despite the weight being lower than the recommended weight .
I fly my GEE BEE with a APC 14x6 prop and are using 15% Motul "micro" all synthetic oil and 5% nitro. I will try a 15x6 APC prtop next time, I have reshaped it so it now has less area than before.
I have not noticed any overheating problems whatsoever despite flying the airplane with minimal intake holes.I also use a secondary muffler made by a mousse aluminium bottle to lower the exhaust noice so it now sounds more scale like.
I did some modifications to the elevator and rudder set-up which is now wire controlled, which is both lighter and stiffer than the original balsa linkage set-up.

Regards!
Jan K
Sweden