[Deanzo]

Jody, of the 8 - 10 260's I've gone cold on, none have been happy with both high gpu and mem at the same time.
ie: same card will do 1022/1191 or 850/1300

Another thing I've found, the mem can bug with the cold, the gpu may well do -100, but the mem may not like -20, it will make the screen look all funny like you posted.
I have well tested this with even stock clocks. But not all of them do this, or it kicks in at another temp.
Only use the temp you have to for X gpu speed, you may well have better luck getting a bit more out of the mem.
And don't let it sit idle for long.