Another thing that will help the idle is a bigger and/or heavier prop. The APC props are heavy but efficient.

This all assumes that you have idealized the idle fuel mixture. Often times the idle mixture needs to be richer than ideal for a good throttle transition. (Walbro even mentions this in their literature.) What I often do is program some exponential into my throttle channel in the radio so that the throttle doesn't slam open so fast. Moving the throttle stick on the transmitter slower works as well. Then you can lean the idle to a better mixture which will also permit a lower idle speed.

AV8TOR