it fails after a few minutes
How exactly. Which fail?
Catalyst crash?
cgminer crash?
BSOD?
Today when I had an unstable system it was VERY useful to have hwinfo64 do a log file, so later I could see which card was the culprit. I raised the voltage on that a bit, and all was fine.
but I think thats a driver issue, ran out of time last night to try and sort it but even though its working if I open the AMD catalyst it's saying the 2 R9's are disabled so somethings still screwed up as I have 13.12 and 2.7 installed and the command line they seem to be recognised. Getting pretty close now at least.
It's weird how often I needed to reinstall the Catalyst after hardware changes.
Try completely uninstall, reinstall.
GL !