UDATE ON POWERING THE GRIDS WITH 5v
I found it ran nicely at stock settings - 650 mhz .
Pulled 0.77A and had a DVD volatge of 1.46. hash rate of about 250. For some reson reason the though i was only able to get one type of grid running with 5v. The newer type wiht the SMD leds.
Once modded though the hasrate dropped through the floor BIG TIME! went down to about 20-70! ouch! so back to 12 v it was.
So basically anyone runnign these at stock no overcloking or modding - why woud you though! - can run these on 5v wihtout effecting the hasrate and save on enery costs.

summary stock (no modsS!!! ) 650 - never tested 850 sorry - runs fine (SMD LED version only).
DO NOT run a modded grid on 5V your hashrate suffers.Even at 650!