OS 91 FX in UK
 

You're probably fed up with queries about 91 FX reliability, but I am somewhat unnerved by all the stories about overheating leading to engine cuts in flight. I operate in the UK and am unclear as to whether I should be following your US advice (ie use a 13 x 8 prop) or the Japanese advice (use a 15 x 8 for sports flying). Noise is not a particular problem for me as I fly from a military airfield. All I want is the most reliable set up. I would be grateful for your recommendation.

OS 91 FX in UK
 

I have one, had it on a Hangar 9 ultrastick 60. Flew it for three months on a 15x8 (various brands). I eventually went to a smaller diameter due to landing gear length and props breaking.

I have never had any overheating problems with the engine on the 15x8 props.