Pretty much night and day. I have a 560Ti and have been looking at going to the GTX 760 for about 30 days or so now. In a recent thread, we came to the conclusion that two 560Ti's would be about on par or just under a single 760m GPU due to the 128-bit memory interface on the mobile GPU. A single desktop GTX 760 2GB has the 256-bit memory interface and would easily perform better than two 560Ti's, without a doubt so you can add 30-40% performance on top of that for a second 760 in SLI.
Thank you. I've been looking at them for about the same amount of time.