replace stock gearset to a highspeed gearset, adjust the AoE of piston teeth and sector gear teeth, use a spring lower than sp120 or m120, install sector chip, keep the piston body and piston head light (use polycarbonate parts) and bearing bushings.. ROF should be high even with just a 9.6v 1400mAh battery..
or
sp130 or sp120 spring, high speed motor, AoE mods, sector chip, polycarb piston set, metal bushings, stock gearset, 11.1v lipoly battery
for motors, go with guarder red motor, JG silver magnet motor.. but if budget permits, go for systema magnum

when using a high speed gearset, avoid springs higher than sp110/m110..
also with bearing bushings avoid springs higher than sp120/m120 unless its a 7mm or 8mm