Vista - which card to use?

I am running an amd x 2 4400 cpu on an am2 board with 4 gigs of rams. My os is home basic 64-bit with directx 10 installed. I have a 7900gs installed with the latest 64-bit drivers from the nvidia dl page. At times I get white horizontal lines flashing across the screen. Ocassionally I get a message that my pc has recovered from an error caused by my nvidia drivers.
I also have a 8600gt available that I could install in the place of the 7900gs. The cards are nearly identical on most reviews as far as gaming performance. My question is would I be better off using the 8600gt because it has support for directx 10 while the 7900gs is listed as directx 9 supported. Is the problem in the drivers from nvidia?
What would you do?

I did a google search and found pretty much the same answer: It depends, do you want Dx 10 support, or not?

The 7900GS seems to be the better card, both faster and more easily overclockable (if you're into that sort of thing)....

8600GT vs 7900GS - EXTREME Overclocking Forums

7900gs vs. 8600gt which one to buy?

http://www.tomshardware.com/forum/24...-7900gs-8600gt