YS110 turning an APC 16x6 @ 9,750 RPM (max peak is 10,300 RPM), using Cool Power 30% heli ... awesome fun for my 9+ lbs Funtana 90. I would not mind a bit more power ...

Gilles - try to prop the engine to get it to turn at about 9,500 - 9,750 RPM. My YS110 is not very impressive when it turns at 9,300 RPM, the difference in performance between 9,750 and 9,300 is way too obvious. Again, what sort of a plane is yours? If its an aerobatic plane like Extra SU then go for 16x8 for a start, if you are going for something like a pattern try the 15x10 ... I got a 14x12 for my YS and I wonder what sort of a plane would it be for? Pattern too?