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I will be running three 5830s on one of my rigs soon. Do you think it will be fine with a 630 watt PSU, or should I look into a 750?

Single 50 amp rail. This would be the PSU I would run them on: http://www.newegg.com/Product/Product.aspx?Item=N82E16817182200

1000/300, v1.163

Not at 1,000Mhz GPU Clocks unfortunately.
(I have tried Sapphire 5830 Extremes @ 980 GPU/180 MEM x3 cards, Sempron 145 on a Corsair 600W and they failed)
....although that same machine & Corsair 600W PSU is running a pair of (2x) 7970's @ 1100 GPU/950 MEM right now without a problem and has been all night....LOL

It's cutting it kind of close OP, but it "should" work.

my 4 card set up 950/300 with sempron,1gb ram, and running bamt from usb draws 750 just for info to go by, or not lol

I have 2 5830 1010/300 Athlon, 1gb ram, with an HD running on a 450watt PSU, pulling 400w from the wall.

i would think you 'should' be safe if your PC is otherwise lightly loaded.  i have 4 old P4 systems on BAMT using this 400W PS http://www.newegg.com/Product/Product.aspx?Item=N82E16817371029 each with 2 x 5830's (930/300 1.163).  i also have a 5 x 5830 system that uses 830W.  when i was ramping up on the 5x system it seemed that each incremental card added 140W on average.

3x5830 + 2x5870 split between 2 old inefficient power supplies all undervolted with max clock on a per card basis = 630 watts @ wall and 1.53 Ghash/sec

I will try dropping to these clocks to hopefully lower how much power (watts) I am drawing.
900/300 v0.95

I have another machine that runs three, stable with 1000/300 v1.163 on a 750watt. I will use this machine to help find a good clock to lower the power intake. Will post results within a few hours...

900 MHz on 0.95v is probably unlikely. Out of 6 5830's, only one peaks at 900 on the dot. The other 5 range from 700-780. Also suggest using 128 worksize and a memory speed of somewhere between 145-175. My 900 MHz 5830 gets peak mhash at 175 memory at 128 worksize. 256 benefits more from 300+ but thats also more electricity.

i run three at 920/195 @ 290mhash or so at 1.063v, performance level 2

three 5830 on 630w would be fine even overclocked i'd think, if you ran it off a usb stick, had no peripherals, underclocked the MB and single core CPU, turned off onboard audio, serial port, and anything else you didnt need, and used a rly energy efficient monitor (~15 watts)

Alright, so I am running at these clocks on the 650watt rig so far:
800/300, v1.4 (wasn't stable at 1.125; 0.95 crashed in less then a few seconds)

It's been stable for a little over 24 hours. Pulling 420w from the wall. Each card is getting about 260MH/s, with a total of 780 MH/s. Will buy a 750w in a month or two so I can run each card at 330MH/s. (Using BAMT for everything)

1.14, right?

I think for a sapphire extreme at least, the wattage being drawn is the same for anything up to 0.95, then 0.951 to 1.063 then 1.063 to (whatever?  or is there another step after 1.163?)

1.4 volts will kill a card within a day, no matter what cooling you have, even liquid helium. I really hope you meant 1.14.
Also like I said, dont expect 900 MHz to work with 0.95v, You can expect a more realistic number of 700-800MHz tops, maybe 850 if you have a freakishly good quality asic. If you go from 800 @ 1.14v to 700 @ 0.95v, it should be about 39% less electricity consumed with a loss of 12.5% mhash. This is still a 26% increase of MH/J. These numbers are based solely on core frequency and core volts, mind. You will get even better efficiency with the lower temperatures that come with running a lower voltage, and more on top of that if you choose to run a 128 worksize optimized memory speed (150-180)

It takes some trial and error to see what is stable. What I do is start with 700/300 @ 0.95v, and let it hash for about a minute. If its stable, I increase it by 20MHz, and repeat. Once it crashes, I back up by 5 MHz, and mine until it crashes, and I keep doing that until its about 1 day stable, then I optimize memory (usually gain 2-10 mhash depending on how high I can get the core and how many SPU's are present). If it crashes again, I just decrease core by another 5 MHz. Temperatures should be the least of your worries running 0.95v unless your cards are packed tightly in a case with poor circulation.

Yes, v1.14! My bad gentleman.

I had a similar setup for a while. Using a 600W, it didn't work. Ended up getting a dedicated power supply for the cards and one just for the mobo.

Ordered the same 750w I have been using for my other setup. Will be here Monday. Thanks to everyone who contributed to the thread! :)

It is my understanding that you shouldn't load the PSU to more than 80% capacity. Otherwise you are wasting efficiency and durability.