Prop selection is fairly simple. You want props that let the engine wind up to the rpm that produces best power and, for 3d, a pitch that produces maximum static thrust at that rpm. For example, a 55ax will turn a 12x6 about 12,000 rpm which is good for that engine. So will a 13x4 and a 11x7. For 3d I prefer 4" pitch so the plane won't want to go too fast.Many prefer 6" pitch and I use those on my planes some also. No big differences. If you put a 13x6 on that engine it may reduce the rpm 1000 rpm. The larger prop would produce more thrust if the engine could rev it to 12,000 but it can't and the lower rpm it can generate gives somewhat less thrust. The larger prop will spin up slower when you pop open the throttle. Slow spin up is annoying.
The preceding is an example. I don't know exactly what rpm a 55ax will spin a 12x6 , maybe 12,500. It doesn't matter.
I fly a Mojo with a OS 50 with a 12.25x3.75w, get about 13,000 rpm and 8 lbs thrust. Good enough for me.