update:
I hooked it up to a different system today. The psu was a good 1000w seasonic and all cables snapped tight into place.
With this as the only card on the system, it booted into windows. Windows 7 recognized it as two 5870 halves in device manager but once I started cgminer it went all berzerk again, black screening and fans to the max. The problem hits instantly once stock non-2d settings are called upon.
Does anyone have other ideas what has caused this, and/or more possible fixes ?
Seeing that the card was good until recently, I doubt this helps. But there is a known issue with some 5xxx cards(I have experienced it myself) with the memory voltage dropping and spiking to quick, and basically giving out grey/red/black screens.
The easy fix, which isn't a sure-fire bet, would be to use triXX to "Force constant voltage".