Upgrade suggestions (To SLI or not to SLI?)

Picked up a 560Ti this summer on clearance and built a nice little desktop home for it. Now I want to go 3D it's holding me back :)


i5-3570K on an ASRock Extreme 6 with 8GB DDR3 1600

If I pick up another 560Ti ($~180 on newegg right now) and run SLI will that be better then putting that money towards a more powerful single card, maybe with more ram?

When should I be worried about CPU bottlenecking? Everything is stock clock speed right now. 

My advise sell the 560ti and get a 670-680 for 3d gaming.