Re: should I buy a 680 or another 560ti and wait till 7 series?
It's up to you. My 560 Ti does a great job on my 1920x1200 monitor. I am not a huge AA/AF fan though, so the memory limitation doesn't bother me. If you want to get into a lot of AA/AF, I'd get a card (or two) with at least 2GB of memory.
Upgrading to a single 680 would be a nice little performance boost. We won't see the 7-series until at least the end of the year.