Pickup a 260 that is built on the Ref 275 PCB. OCP was the first thing I had to mod. It crippled the card to 2D clocks with stock voltage. Got her running 810 core and 1728 shader with 1.25v so far on water. No sub-z cooling for me yet, but I think she's got some more room on water tho.
http://i170.photobucket.com/albums/u...l/modshot4.jpg
EDIT: Just tried to do some tuning. The card is acting wierd. When I increase the GPU core to 1.33v during load, it shuts the memory controller down. The memory is running stock voltage/clocks. The GPU controller is ADP4100 and the memory is uP6161. I'read the ADP datasheet, but it doesn't give any clues as to why the memory controller is shutting down. Anyone got any ideas?