I've been having trouble with my GTX970 since the 311 update. It won't render using GPU acceleration at all, and it prevents me from using Neat Video's GPU acceleration if the Vegas GPU timeline acceleration is turned on. Up until now I didn't have any issues (as long as Neat Video wasn't configured to use 100% of VRAM, I dialed it back to 75% and all worked great). Since the update, though, there are lots of issues. This video details what has been happening.