The 560 I got is free as I paid for the upgrade to my son's gammer PC.
But I don't see the 560 listed on the GPU list.
I assume a 560 not as good as a 580.
If I can add the 560 to my main PC that has a 680 would that combination add much to the processing speed of that PC?
I guess the question is what is the best thing to do with a free 560?
As you can see from the chart, if you add that 560 Ti to your your 680 and you are running Premiere 7 (CC) it could be a help, if you are using "a lot GPU accelerated effects and/or features" often like down scaling HD to DVD or HD to a lower resolution H.264 format.
But first check your power supply to make sure you have a additional 170 watts available for the GTX 560 Ti or 210 watts if it happens to be a 448 core version