One of my 5970 cores hums along at 860MHz while -undervolted- to 1v. The other core is a different story though. 2 out of 3 VRM chips are dead. Can only push about 0.95v through it at greatly reduced core clocks to get it to work without crashing the entire computer. I run it at 0.85v instead though (and 485 core) to keep VRM temperature in check though.
OCL 4 = 5970 @ 860 1v, OCL 5 = 5970 @ 485 0.85v