What r u trying to tell me? I shouldn't SLI/CFx?
That's up to you. Just be aware going in that there are issues with both SLI and Crossfire. Also keep in mind that the 560 only has a single bridge so upgrading to a 3x solution which would eliminate micro-stuttering isn't possible.
Personally, I'd opt for a single 580. While it won't have the raw performance of 2x 560ti, it's awfully close and you don't have to worry about games that don't support SLI, or microstuttering, or mismatched drivers, or 2x the failure rate, excessive heat, excessive power draw or the multitude of other issues associated with multi-gpu setups.