My .46NT pulls a 12.25x3.75 with plenty of power. It has a Tower muffler on it and that gave it another 1000 RPM.

I wouldn't say in advance that the 11x6 blade would over load the engine, but I would suspect such a thing until I actually saw how it performed. Tach your engine well with something like a 11x7, or similar, and then try the 3 bladed prop and see how it tachs. You are going to be borderline with that prop and won't know until you try. Like W8YE said, maybe a 10x6 would be worth trying out too. Props are funny things. Maybe both will fly like crap. You really have to experiment.

Something that W8YE suggested for my 46NT- try either the OS A3 or Tower plug if you are using an OS 8. That was a world of improvement in my engine. I'll never go back to the OS 8.

I have both the .46NT and the .45 trainer system engine. Both are really superb engines that put out a lot of power. The .45 is an incredible deal at the prices they sell for.