HV servos are good if you are running HV all-around... if you are using a std throttle servo you can use one of these
http://www.spektrumrc.com/Products/D...odID=SPMVR5203 ...i predict servo companies will do away with HV servos due to the popularity of A123 and Life batteries
from 4.8 to 6v you can expect about a 20-25 % increase in power based