Originally Posted by pharcycle
i suppose if you wanted to be absolutely conservative and get a quick answer then if you measure the power drawn by the card (or maybe the delta between idle and full GPU load) then since the card can't produce a greater heat load than power drawn (otherwise you'd have a perpetual motion machine) then a heatsink that can handle that power will be fine.
There isn't going to be a generic formula for heat output though. One thing you could maybe do is use the relation that P = V (squared) / R. since R is near enough constant the power will increase by the voltage squared.
If, say, it requires 250W of cooling at 1.2vcore then at 1.3vcore it would require 293W.
However there are many, many more factors that will come into play and really the only way to know would be to measure it.
That's a decent approximation, but transistors have a nasty habit of being nonlinear
Have you tried HWInfo64? My 7950 has a bunch of current sensors for the GPU, memory, VRMs and such. If your 6970 does, you can just multiply the current and voltage of various onboard components to get a very accurate power measurement.