hello. so im thinking about selling my 2 gtx 470's. i have been using them together in sli, and they are truly great. but im affraid if i keep them much longer, i wont be able to get much out of them to put towards a more up to date card. is what im wondering is, how much longer will these cards be able to keep up with games be fore i will deffinatly need to upgrade? i play at 1080p, with maxed out settings, mandatory. What card should i get to replace them both, that will give me at least or close to the same performance? And if i were to sell them both, how much for each? thanks for the opinions, and the help in guidance.