Strange that it crashes with just one gpu. Tried each one on it's own in the system? So truly take one at a time out.
Other thing you might try is instead of the latest crimson drivers use older drivers. I think for my HD 7870 (Tahiti LE),when still using them, i stopped updating at about Catalyst version 15.4/15,7.
http://www.guru3d.com/files-categories/videocards-ati-catalyst-vista-win-7.html
At least when wanting to try look at the Catalyst versions first.