The APC 12.25x3.75 is a very wide and heavy prop. Much different than the 12x4. I found that it spools up very slowly when you throttle up. I found this to be true (at least not to my liking) on a well broken in motor unlike what isaacslaw said. I gave them all away. The APC 12x4 is my favorite 3d prop for this motor but have run 11x4's as well. On non-3d stuff, I prefer the 11x5.

Mike