I'm in the process of building a gaming pc and I've come across the EVGA GTX 660 superclocked gpu's and I was wondering how SLI GTX 660's would compare to a single MSI Twin Frozr GTX 680 OC. I could save around $90 if I go with the 660's. Also, if I did get the 660's would I need more case fans due to more heat generated or not? Thanks in advance