Your performance should be the same.

When going from a 2 blade prop to a 3 blade prop, either drop 1" in diameter OR 1" in pitch. When going from a 3 blade to a 2 blade either add 1" in diameter OR 1" in pitch.

Multi blade props are not efficient and most people would not suggest them unless you need ground clearance.

FWIW - MOST people run a 12x6 or 12x7 APC on a 61 engine. The additional pitch will prevent you from over revving the engine while providing a little more power.

I suggest checking your rpms with both the 12x5 and a 12x6 or 12x7 before flying the bird. Remember, the engine is going to "unload" in flight so you will pick up a couple of hundred rpms.