If you switch to a 20x8 APC, NX or Menz propeller you will see a great improvement.
ORIGINAL: Superfast
As far as the prop, I am using a Zinger Pro 20x8. I an currently turning it at 7400 rpm. I can probably get it to increase a little once the engine breaks in some more. I now have about 8 flights on the new engine and haven't had to touch the carb needles yet ! Once I get about 2 gallons through it I will give it a little tweek and see if the rpms increase.
Scott