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The best version of a graphics driver is the most recent one your card supports. I have never seen a permanent performance drop due to updating graphics drivers, if one does happen the issue that caused it is fixed in the next update.
Nvidia uses a "unified" driver scheme - their one driver supports all GPU products. The consequence is that there are frequent driver releases (including beta releases) to support new products and fix bugs. But there is always the danger of breaking older HW or regressions. Hence the advice of sticking to particular version for particular HW. Use the "most recent one" at your own risk. Nvidia broke the video deinterlacing capability for the 7300GT, and took more than a year's worth of releases before restoring it.