The GTX 560 Ti, is a nice Fermi Architecture card.
Had one GTX 560 Ti (384 Cuda core), which was perfectly with GPU and CUDA in Sony Vegas pro -
then I switched to a GTX 660 Ti Architecture card (1344 Cuda cores). The GTX 660 Ti, was okay for Premiere Pro - but not for Sony Vegas !
The GTX 660 Ti was a no go for Mainconcept - Sony change the AVC template, so the GTX 660 Ti, was okay for GPU rendering !
Sony Vegas Pro 12 (Build 563) 64bit - used 9 stk. H.264 (.mts) 24Mbits footage - length 01:00 min.
According to Sony - the Sony AVC template, in Sony Vegas Pro 12 build 563, was a beta Kepler version !
Couple thing to consider when switching NV to AMD.
Make sure the to not run both cards in the same system, even though the x58 has the lanes to support both in X16. I think there was someone that used to run AMD and NV cards with Vegas, but I would think there would be more crashes in that configuration.
Uninstall the NV software/drivers before pulling the card out of the machine. Make sure to get the GPU back to the default windows driver, such that is stays after a reboot. Then shut the machine down and install the other card.
Its just important to remove as much of the old driver as you can.
Its a good time to verify your OS files with SCF /scannow, run memtest86 to verify your memory is still good, run CCleaner after removing the old GPU, and make sure all the windows updates/Bios are pushed. Verify OpenCL operation with something like Luxmark, or the Min/Max Vegas plugin playback while monitoring your GPU load.