560 Ti Superclocked SLI vs 660 Ti Superclocked

560 Ti SLI will be slightly faster.

Regardless of that, I will suggest the 660 Ti, because I always recommend a single card over a dual card configuration as I am not a fan of SLI or CF. So, get yourself a 660 Ti. I have heard many driver or overheating problem with dual card (CF or SLI) configs.

If you have a 560 Ti already, That will be another different story. I think you should get another 560 Ti instead.
 

cmersits

Honorable
Aug 24, 2012
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560 Ti has only 1 GB VRAM, 660 Ti has 2 GB. 2 x 560 Ti will be severely bottle-necked by the 1 GB VRAM. Go with a 660 Ti, then you can always go SLI in like a year or so.