Normally when I see that kind of artefacting I'd say you tried overclocking your graphics card and the memory got damaged.
The nVidia 8500's seem to work well with SU, so my first port of call would be to try a diffrent driver. Try installing the latest driver. If you are already using the latest driver, then try an earlier driver (from say a few months ago). Failing that I'd have the graphics card tested.
Also, I'm not really aware of any hardware that'll make SU scream. For the some or other really really really stupid reason SU doesn't support contemporary hardware the way it should. You'll be better off with a highly clocked CPU (dual and quad core CPU's don't directly relate to better performance in SU6 ATM - might just help with other apps running in the background), an 8xxx series nVidia graphics card (the 8800 GTX really rocks for a gaming class card) and between 2 and 4GB of RAM (depending on your usage and OS). Since your machine complies to most of the previous, I wouldn't spend my money on a new machine just yet, wait until SU7 sees the light of day to see if the situation changes.