Guessing HP curves from prop values is useless unless we know exactly how much power the prop requires. Take Dar's example above. The peak HP value appears to be the same however it's 800RPM(really 1600RPM) different with different props. The engine is not changing it's torque curve. The above only proves that the prop constants or pitches are not accurate. This engine's peak torque should occur near 2500-3000 prop RPM. It should not be at 4,400 RPM like this indicates.

For example the Graupner 12x6 is well below Pe's estimates for power absorption. This is due to the fact that it's really closer to 5.5" pitch not the marked 6".

Since you have the ability to adjust he pitch to whatever you want I would try flying it at many different setting and see what works best. That engine should not be prone to detonation based on the design, so you shouldn't have to worry about that.