I simply do not believe that my old Radeon 4850 had double precision but my new 6790 does not. Is milkyway wrong when it says "An ATI GPU supporting double precision math is required"?

from the 6000 series, only the 69xx do double precision. It's only the high end cards of a series that has double, not much to do with newer or older.
See GPU requirements

Yes Peter... gotta be careful mate.

I had 2 x 4770's running (still have them here in the "useful parts" drawer) and they are dbl precision.

I have 2 x 5850's in my other i7-920 and when I went to "add to" (new MSI X58- Pro E board has 3 slots)these 4770's, I checked every 6xxx series card AT the AMD site for which were dbl precision.

Settled on the 6950.... problem is, the 650 W PSU wont drive the 6950 plus even ONE of the 4770's !

(also, watch ut with multiple GPU's if you ever run Moo, as it uses both in the one WU and waits until the slower one finishes before starting...)

Sadly, unless you are happy to use that card on other projects which dont require dbl precision (or more so "need" it) you will have to try to sell that one and upgrade... chalk it down to experience.

Settled on the 6950.... problem is, the 650 W PSU wont drive the 6950 plus even ONE of the 4770's

What 650w are you using? Quality PSUs are essential. I have no problem running X6 machines with 2 5850 cards or 1 5870/5850 & 1 460GTX on either XFX or Antec 650w PSUs. Had one machine running for a long time with a 4770 and a 460 on an Antec 500 EA PSU. It drew 400w according to the killawatt and never had a problem with it. The 4770 (have had 10 of them) uses <100w at 99% utilization, the 5850 about double, the 460GTX a bit more than the 5850. As I understand it the 4770 had the additional capabilities such as DP because it was the test bed for the 40nm process at ATI/AMD. It still offers good performance/watt along with the 58xx and 69xx series.

Indeed, I've elected to stay with a collection of 4770, 4830 and 4850 cards. To get double precision in newer AMD cards, you have to lay out a fair amount of change (you can pick up used 4850's for under $60 - or $90 out of pocket if you elect to replace the heatsink/fan with something new). Besides, the top end double precision cards, besides being very expensive do draw quite a bit more power. I can run the 4850's with a solid 500W to 600W power supply easily, and figure if I went with the 6950 I'd have to push up the PS as well.

Yes Peter... gotta be careful mate.

I had 2 x 4770's running (still have them here in the "useful parts" drawer) and they are dbl precision.

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I wonder what power of PSU on needs to run a dual HD6990 set up? That is 2 x HD6990 with each HD6990 running a double HD6970 card under the same cover.

Just wondering!

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Go away, I was asleep

Would be interesting, remember to include the cost of a dedicated circuit as well along with the batch of fans.

I wonder what power of PSU on needs to run a dual HD6990 set up? That is 2 x HD6990 with each HD6990 running a double HD6970 card under the same cover.

Just wondering!

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Nice piece of daydreaming John! I confirm the performance of the 4770 cards. I now have 4 and they perform almost as well as the 4850's, running cooler, and with lower power requirements. In terms of bangs for bucks they are good value.

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Don't drink water, that's the stuff that rusts pipes