Doing some comparisons and I'm trying to find a good standard rule of thumb on how much power a 5870, and a 5970, would each use under load? I understand an 850w PSU would run 2 5970's, would that also run 4 5870's?

In my attic I have 8 5870s divided over 3 machines.

All are clocked at 945MHz - about 11% over standard clock.

The total power use, at the wall socket, is 1900 Watts, so slightly under 240W per card of mains power.

Assuming the power supplies are 85% efficient, and ignoring power use for CPUs, HDDs, chipsets, each 5870 might be estimated as using slightly over 200W.

This crude approximation suggests that your 850W power supply can probably run 4 5870s, but you would be

**very** close to its maximum output, particularly if you overclock the cards.