With modern engines the name of the game is all the RPM you can get.
The historic engines seem to have a rather low RPM limit and smaller props don't help. You might do better with a 9/7.
I'm not sure excess oil really hurts, either. The excess oil takes up volume in the chamber. If the engine is set up for 29% it will run best on 29%. The needle is set to the amount of fuel that the air will burn. Excess oil will reduce your run time for sure, but maybe not your power.