I'm not sure if this is related to your problem, but when I installed VP13 last week I forgot to set VP's internal memory usage from 1024 to 2048. As such, HitFilm was causing me all sorts of problems. After I fixed it, all behaved well. Note that I am referring to the setting called "Memory needed by Vegas 64-bit" on the Internal tab of the options menu.
I have been for ages on driver 296.10 and only recently moved up to 334.89 and I will stay on it for ages again. Don't change driver unless an app specifically calls for it and certainly don't let Windows do an automatic update on anything.
I was heretofore under the impression that if a driver is new then it brings with it added features.
New drivers can fix existing bugs, and can have new bugs of their own. They can expose existing bugs in supposedly currently working/correct code.
For example, in NewBlue Titler Pro 2 a new AMD driver "caused" a problem with the display of the first letter of text. It was dimmed. It worked fine with the previous driver. I reported this to NewBlue and to AMD. In a subsequent NewBlue release the problem was gone, fixed, and I had not changed the driver or Vegas version.
If you are having no problems with a driver, then it is usually best to stay with it. If you have occasional GPU crashes it is worth trying new drivers and new Vegas versions.