I usually run the APC 5.5 x 2.5 prop and get about 20K on 10% Nitro using Merlin Plugs with an extra gasket. APC made a variety of 5.7 x 3 props, some smaller, some larger, so I can't exactly comment on your engine's performance.
If it runs strongly through an entire flight, it is just fine. If it burns plugs, the crankshaft is probably tight (seen two like that). If it blows fuel out the "nose" of the crankshaft, it is too loose and needs to be exchanged (only happened to me once, but there was no hassle in getting a new one).
A consistent problem that bit me again today is having the venturi screws come loose (vanish, actually). I think that Locktite must be dissolved by Nitro. I will JB weld my venturis in going forward.