I found one reviewhttp://www.fudzilla.com/reviews/item/24458-point-of-view-/-tgt-gtx-570-beast-2-reviewed
Check it out.
For me getting the 1280MB is fine and oh course somewhat this is not worth it and then this is my opinion. Yours might be different. I will get 1280MB with aftermarket nice and good cooler if I have the money and I will not buy the 2560MB because it's a better way to safe money. Or I can just get nice 6970 (with aftermarket cooler of course) and OC it, it will maybe outperform GTX 580.