If alot of users have a single 580 and were told SLI works and increases performance by about 50% = more planes on screen / better FPS, would they upgrade ? i suspect the answer would be YES! (as soon as I get some money)
Why waste a perfectly good 580 to upgrade to a 680 when a second 580 would do the job - the 580 is a great card! Like comparing spits and mozzys.
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