Yea, do that, then after you reach the maximum OC go download FURMARK, (http://www.geeks3d.com/20120510/furmark-1-10-1-gpu-burn-in-stress-test-videocard-geforce-radeon/) the latest version, and see if it's stable for a couple of minutes, like 5 or even 10+ if you want to be sure, but closely look at the temperature and other values in the furmark window, if you see "core: 899 (throttling" and you put in 900mhz or something like that then you must lower it until it's stable, if it throttles itself then it must mean it's unstable for gaming, and look at the temperature too, it shouldn't be something absurd like 90-100, if It's lower than 80 I think it's perfect. Idle should be around 30-40 I guess. If it's stable in furmark for 10mins then no game should cause it to overheat, shut down or anything like that. Also don't increase voltage yet, I don't think it can be of much use except to cause heat in your card, or stability issues.
Also why does it need 2gb? makes me wonder, not even most gtx580 had that ram in the 5xx generation, it had 1.5 i recall. I know it's slower gddr3 but it's obviously not built for running games on 3 monitors... It's like cooling your HDD with liquid helium, why? It's completely useless and lower memory could've probably made the card be more "green". For anybody reading this thread: memory means nothing, just look at benchmarks if you want a good card. Look at a game you like and look at its benchmarks if card X has 60fps or 120fps if you have a 3d monitor, then it's perfect. Yes I know memory matters but most midrange/highend have an abundance of free memory in any game except at gargantuan resolution, but if you've got the money and will to get 3 monitors, then you probably know what card's the best at playing games on that.