YS made engines specificaly designed for nitro content up to 50%. The internals were modified to run this fuel. I doubt further increases in nitro would result in much if any increase in speed other wise everyone would be running it. Lots of people get in the mindset that more is better often passing the saturation point where any advantage can be gleaned but they firmly remain convinced otherwise.
I may not race these motors but have been around racing and performance engines long enough to know that if any one thing made as much difference as you claim everyone would be doing it not just a few of you otherwise the others might as well stay home. This goes for fuel, engine mods, frame or any other deviation from the norm. Anything that actually gives an advantage is adopted pretty quickly or there is no sense in taking the horse out of the barn so to speak. That only a few of you resort to such high nitro content means the advantage does not prove out on the race course. Just saying!!!!!