I use a MARK III in my SIG 552 to set the ROF and find 11.1v fine to use. At least with a M110 spring this set up is holding fine. Oh and as far as I'm concerned a PEQ is just a way to make your gun unbalanced, the fancy way is the grenade launcher
All in all I have to say that DonP can hook you up with that MARK III and its a life saver on all your components, nearly a must for lipo if you want peace of mind.