I Didn't read through all the posts, but what i did glance through i found little to no mention that you have to reinstall your graphics drivers after a bios flash.
Your cards may appear to function properly even during stress tests but flashing the bios corrupts the driver and causes to to hang every10 min or so in game. At least in my case. So if you Experience problems Re-Install gpu drivers.
I would also like to note if you have a sli setup, it is totally not necessary to flash one card at a time as stated in the main post. Just do nvflash -5 -6 blank.rom . You will automatically be prompted to flash both cards, hit Y in both instances.
I will also Note that someone mentions the only really boost with bios is compatibilty/stability, Stability= highier clock. Specificly with a bios that unlocks your voltage control you can achieve an overclock where voltage was stopping you from pushing further. This requires you to edit and modify your bios yourself.
I probably should of known to reinstall my drivers after a flash... but successful stress test fooled me into a stupefied state of bliss which left me playing guessing games with my cards crashing in bf3 at any clock.
All is well now with unlocked gtx 460's SlI @900Mhz1.112v 71c full load 40-50 idle:wave2: