Maxam, I have the prop constant for the Mejzlik. I'll post it for you tomorrow
I wouldn't doubt based on what I'm seeing, that it's pushing 5HP. Very large gains with my setup and 16% nitro.
I don't pin the throttle for more than a small handful of seconds at most, so not too worried. Mostly fly at half throttle or so; and it seems to cope well anyhow without overheating, as well as I am checking valve clearance regularly. The rated RPM is on the ground as well don't forget... David Payne of Horizon runs his off onboard glow, with a 22x12 Mejzlik, pushing 6,250 on the ground and recommends that setup.
For what it's worth, my engine with a 22x12 was pushing dangerously close to hitting 7,000rpm - I stopped after I saw a peak of 6,900 and something briefly!