We use
this motherboard. Works with 5 cards using those PCIe/USB risers. Find a cheap CPU and a single 8GB RAM stick. We use 2 of
these PSUs, as you can run 5 undervolted 280x on only 2 of them, which will get you 3.5MH/s per rig, @ ~1250-1300W, and ~$2500 per rig.
Thanks for the awesome advice! So this motherboard should work with 5 Radeon 7950's, or do you recommend the 280x's?
Yes, it should work with 5 of any GPU. We've got 3 identical rigs using that MB with 290s or 280xs.
I'd recommend a 280x over a 7950. With a 7950, you're looking at either buying used, or paying the same price for a new one as a 280x. The 280x is compatible with VBE7, which is nice (as opposed to the 290s, which are voltage locked no matter what).
at this point demand for these cards are raising prices everywhere and are backordered in most places in the US. buy what you can at a reasonable price; i've seen 280x being sold for $600. people are taking crazy pills.
if you can manage the heat and the expense, get the 280x. it will be fewer cards for the same hashrate as an equivalent rig with 7950s. you could run 4x 280x with 1600w (2x800w) power supplies.
if you want to fuck around with your settings, i like the 7950s bios selector switch to allow for custom card voltage. in a multicard setup this could save money with slightly smaller wattage power supplies. the 1000w+ power supplies are ridiculously expensive.
The problem is no matter what GPU you buy, they're WAY overpriced. I bought a pair of 7950s six months ago for $200/each, mined on them, and then sold them for $300/each. Those 280x MSRP for $299, but are selling for >$400 on almost every website. $500 for a 290 and $600 for a 290x are just crazy.
And yes, 2x800W would work fine. I'm running 2x750W, and pulling <1300W from the wall.
Almost every AMD GPU will have a dual BIOS switch, which will allow you to save the BIOS, tweak it in VBE7, and flash your modified, lower voltage BIOS while still having a backup. That's not something specific to the 7950s.
