Think of the gain as a trim.... You want to get this as close to spiking as possible(if there is a discernable difference in spool noticed), without actually overshooting your target. Typically, if the start boost is set high enough and the gain is at a moderate level(start with 15 and work your way up), you will see very little(if any) improvement once you hit the sweet spot(which might be around 50% gain... not sure on your setup). Having the gain set correctly will also help to reduce the tendency to spike much higher in cooler weather also.

Justin