The chain saws these things are made from routinely rev to over 10,000...There's a small Husky that's advertised to turn 15,000 rpm unloaded...I don't think we need to worry about 8000 rpm being too high.....
Repair manual for the Zenoah 62 cc chainsaw says to check rpm on the saw, don't go over 13,500 unloaded..The chainsaw cranks WILL stand it..Maybe Brison, Fox, Fpe, etc are concerned that their cranks and rods won't take it.....
In 15 years of playing around with gassers I have not heard any detonation...Timing much over 30 degrees results in missing and slowing down..I HAVE seen holes in pistons from too much nitro in glow conversions....Any engine timed far enough advanced for detonation would't run very well anyway, regardless of octane....I ran some 100LL from the airport, not much difference....
Right TKG ????