That website's compare of cards is a terrible way to look at real world performance. The 680 (or 7970 as well) are usually on par or a little slower than the 590 and 6990 in games. The 5970 of course runs slower than the 6990 which should give you an idea of where the 680 lands.
http://www.anandtech.com/bench/Product/165
http://www.anandtech.com/bench/Product/508
It's hard to compare the two since there are no side by side charts but if you look at crysis on the two links, the 7970 is just a few frames behind the 5970. The 680 is a little faster so I'm guessing it's on par with the 5970. If you've had CF related issues or stuttering i'd say upgrade if it's an issue. otherwise the performance difference isn't large enough, wait for 690 or 7990?
Of course your mileage may vary depending on the benchmark