A nose heavy plane takes more elevator throw to turn and slows down more in the turns than a plane with a rearward cg.

Keep moving the CG back until it starts to get squirlly. You don't want it squirlly, but you want it as close to that and still be controllable.

Don't get too hung up on ground rpm. What matters is how a motor unloads in the air, a plane with a cleaner airframe will unload better than a dirty one.

The speed secrets thread may help with ideas in cleaning up your airframe and prop maintenance. The series of articles can be found here. They are a couple years old, but still contain a few ideas that may help you out.

http://www.rcuniverse.com/forum/m_3980534/tm.htm