Mitch, without a dyno you will never know the motor's sweetspot. However, you can play with extra advance and you'll hear the motor really sing when it winds out... Its a game of diminishing returns and the battery will dump quicker and the brushes/comm wears quicker!

I found the trickiest bit is deciding whether to change the gearing or the timing of the motor as both can be fine tuned to get the desired balance of punch and top speed.