Hi robbstart,
Similar problems have been reported here by others. I have the same problems and have not been able to upgrade past the 8.92 drivers that came with the 7970 cards. The common point is multiple 7000 series cards, often with a headless card, mostly on Windows 7, A general summary:
8.92 - works fine
8.95 - all releases (up through most recent) frequent crashing, BSOD, and/or hanging video drivers.
8.96 - all versions run fine no crash/hang. but - headless GPU's clock is stuck at 500MHz and cannot be adjusted.
8.97 - (recent unofficial release) same as 8.96, runs OK, headless GPU clock still stuck at 500MHz.
You said you use a VGA plug for one GPU. It is possible that the 8.96/8.97 500MHz clock issue will not happen when using a plug, you might try one of the 8.96 drivers. They are often released on the popular gaming/over clocking sites.
Please post anything you find interesting.
drallan