I agree with the other guys , you should be around 6800 to 7000. I like a little more but we don't have restrictive mufflers. 22-10 Zingers always worked for me on my 36 pound Corsair. It would loop from level flight with proper throttle management as well as do other scale manuvers. No aerobatic champ but it did it's thing well. They slow down pretty fast at part throttle. I usually landed at at least 1/3rd throttle. Cut just a foot off the ground.

The 20 inch props didn't work very well on the warbird. They worked great onthe aerobatic planes that didn't need all the speed.

I'm looking at the high compression conversion and running on E-85. It is supposed to work very well.