OK, here ya go, get this cooler:
And if you got lines when you OCed, that is your memory. You can not OC that much at all. ag3 OCed his to 360 (720) and I got mine to 370 (740). That is about as high as you can get without added heaksinks to the memory. So you need to move the MHz up a little at a time. If you get any lines, back it down and test again. If you see white "snow" you OCed the GPU to much. If you get the cooler I put in this post (what i have) you will be able to OC the ell out of this. ag3 got his to 430, and I got to 465. The stock is 380, so I am happy. XT speeds are around 410. Let me know if you need anything else.