what about in the ballast itself, is it more efficient to run it at 220 vs 110 if it supports it or is there no real difference?
Magnetic ballasts that are switchable from 110v to 220v are much less efficient @ 110v because they are essentually 220v ballasts. If your ballast is NOT switchable, it is designed to run at the voltage it is. This does not apply to digital ballasts.