I am biased as a YS pilot, but I will try to give an honest observation.
I had the YS60SR in my N5C and my good friend had the OS55HZ-R. We both have the corresponding Hatori muffler, both running Cool Power 30%, same Rail blades, etc.
Mine at break-in settings ran at least one, if not two minutes longer than his with the OS. After two gallons I flew a normal flight with flips, rolls, funnels, etc and it was over 8 minutes long! My buddy is around 5 to 5:30min on his OS.
Power is great on both models, but even if I didn't fly for YS, I would choose it simply because of the incredible fuel economy.