While very light, I find the RMR and others of its ilk to be too unforgiving of sloppy cheekweld (like when shooting from awkward positions).
Either Aimpoint Pro or keep an eye out for a deal on the Aimpoint Micro (I recently picked up a couple of Aimpoint H-1 Micros w/mounts from Palmetto State Armory's for $459/ea shipped and Botach currently has the Aimpoint T-1 Micro w/mount for $525 shipped).
Tomac

