Alright, for anyone who wants hard numbers, here they are!
Both batteries tested on fully upgraded M4, prometheus double torque gears (properly shimmed), prometheus piston, 380fps spring, TUNED motor, low resistance silver plated 18 gauge wire, triggermaster MKIII SW-COMP, deans connectors, bearing piston head and spring guide.
Readings are after a full charge on NiMH and LiPo
The 11.1v LiPo was first tested at 50% motor speed (920rpm), then at 70% I didn't crank it up any higher because there's simply no point in risking internal damage.
11.1v 20C 4900mah LiPo (AT 70% MOTOR SPEED)- 1052rpm
9.6v 4200mah NiMH - 1212rpm
7.4v 20C 1600mah LiPo - 910rpm
9.6v 1600mah NiMH - 1066rpm