You should get like 19-20MH/s with those.
If the temperatures spike as soon as you start mining then its either bad cooling or blown VRM. If you never took it apart before to change the thermal paste then most likely you have a blown VRM.
The GPU mines at 10 MH/s @500MHz (95 C) and @400MHz (85-90 C) and if I start mining the temps go up within seconds from 40 to 85/90 C. Any idea how to unblow the VRM

Damn!