Just use the latest driver from nVidia. No one can tell you what would be the best driver for your system. You just have to do some trail and error.
If I do upgrade to the newest driver and everything seems 'stable' does that mean I should stay with it? Or is their some testing I need to do before settling on the driver? thanks
It has been my experience that newer drivers are mostly for newer cards. There are a range of drivers that work well during a card's popularity. After that it goes from experimental, i.e. install = works better or install = a little worse, to problematic, i.e. install = this is awful or install = BSOD. Using drivers that are contemporary with the 6800 series will usually work best for you.