I'd experiment with higher nitro content fuels, lower pitch props http://www3.towerhobbies.com/cgi-bin...?&I=LXESM8&P=7
and see if you like what you have in the plane already. Problem with changing from OS to an AX or another brand at this point (I do have the same plane, but run a OS 61 SF series on it) is you've cut the cowl for the OS already and another change requires a new cowl or the swiss cheese look, not to mention changing pitts mufflers.

I agree you should just fly it scale and not worry about unlimited vertical on a large wingspan/heavy plane as the chipmunk. Scale plane, scale flying.