However you are confusing prop stall with output power.

Given higher RPM's on an unstalled prop, the engine which produces higher revs produces more work = power.

A 2 stroke .50 turning a 12x6 prop at 12-13k RPM's is not stalling the prop.

Take that prop and put it on a .60 Four Stroker which will turn only 8k to 10k and you get lower output power, hence the need to increase the displacement to compensate.

That is why we don't use a .46 four stroker in place of a .46 2 stroker.

Back to the original poster's question, he gains no power advantage in his plane going for the four stroker, just the added costs. At that size the fuel offset is not that great so as to justify the 4 stroke engine. This of course changes as you move up to the larger size engines, and typically by the time you hit the 1.20 sized engines, you start saving significantly in terms of fuel consumption going to the four strokers.

The small four srtokers may sound nicer though.