400 FPS is pretty hard on a stock V2 gearbox, Systema clone or not. I'd personally prefer installing a lighter spring than a velocity reducer. While it may reduce the muzzle velocity to acceptable gaming levels, it does nothing to help manage the pounding the muzzle of the gearbox gets from that powerful a spring. That's what I'll more than likely do when I receive mine. I was considering installing a stock TM spring, but will most likely go slightly heavier to get into the 320-340 FPS range.