MSI 890FXA-GD70 AM3 AMD 890FX - 5 x PCI Express 2.0 x16

(2 x16, 2 x8, 1 x4) and 1 PCI Express x1 slot.

http://www.newegg.com/Product/Product.aspx?Item=N82E16813130274 - $195

AMD Phenom II X4 840 3.2GHz

http://www.newegg.com/Product/Product.aspx?Item=N82E16819103921 - $105

G.SKILL NS 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1333

http://www.newegg.com/Product/Product.aspx?Item=N82E16820231394 - $40

Seagate Barracuda 7200.12 ST3320418AS 320GB 7200 RPM 16MB Cache SATA 3.0Gb/s

http://www.newegg.com/Product/Product.aspx?Item=N82E16822148469 -$35

Antec TruePower Quattro Series TPQ-1200 OC 1200W - 228A on 6x 12V Rails

http://www.newegg.com/Product/Product.aspx?Item=N82E16817371039 - $239.99

Total for Base System: $615

Multiple 120mm Fans of your choice -$20-$50+

So here's the base system. No case needed really. Throw in some 120mm fans as needed. You have a 5 PCIE slot case. Sure they don't all run at x16, but we're not gaming, we're BTC mining which as I understand requires very little bandwidth, much like Folding at Home. So I'll say that's a moot point. You'll need a PCIE extension ribbon for $5-$20+ to fit in all dual-slot cards. There's also a PCIEx1 slot, which I've read can be modified relatively easily to accommodate another GPU, so for this theoretical build I'm going to include that.

I chose the phenom x4 because running two clients on my dual 5870, with an i7 920 @ 3.8GHz used 12-13% of CPU per client.

Running windows 7 and my 2 clients uses almost 2GB of RAM, so I chose 4GB for this setup.

Cheapo hard drive, not an issue.

As for the PSU, I would think this PSU could handle 5-6 5850's. Estimating each 5850 at ~150W draw each comes out to 900W for 6 cards. Estimate the CPU at ~100W and we have some room for error. Also this one has 12 PCIE 6pin and 8pin connectors, saving us some trouble.

Let's finish this calculation with 6x 5850's.

6x Sapphire Radeon HD 5850 XTREME 1 GB

http://www.amazon.com/Sapphire-Radeon-PCI-Express-Graphics-100282XTREME/dp/B004W75ATI - $900

$900 + $615 = $1515

Now let's breakdown the Mhash/s. I personally have 5870's, not 5850s so I'm going off of my expectations from a similar card and from what I have read around the place. These 5850's seem to be the biggest bang/buck if you are buying NEW. I've seen people pushing 5850's to above 350 and people leaving them at lower. I'm going to assume if you're dropping this much money on such a complicated rig, that you are going to overclock them and be skillful enough to do so.

A 5850 could make ~350Mhash and are ~$150. 2.33-Mhash/$1

A 5870 could make ~400mhash but are ~$200. 2-Mhash/$1

A 5970 could make ~800Mhash but are hard to find and could be anywhere from $500-$800. Let's say you find one for $600. 1.33-Mhash/$1

A 6990 is ~$700 and can make up to ~800Mhash. 1.14-Mhash/$1

A 6870 looks to be maybe $175 and gets ~300Mhash. 1.71Mhash/$1

That's about it for the best cards out there. Of course 5850's are a little less efficient power-wise compared the to 6xxx series, and I'm not taking power into account. But I think overall the 5850's increase productivity will easily pay for it's slightly increased power consumption.

**So we have a $1515 system with 6x5850's @ 350Mhash/s, or 2100Mhash/s.**

So the system overall is 1.386Mhash/$1

So the system overall is 1.386Mhash/$1

Of course I have sacrificed density by going with single card systems. I think going with all 6990's is doable, but at a cost. 6x 6990's = $4200. Let's say you found a good deal and somehow got them for $3900. Well we basically doubled power consumption. Going off the specs of the 6990 being rated for up to 375W, let's say it draws 300W. That's 1800W + the system itself so maybe 2000W to be safe. We'd need a second PSU for ~$150 for a 1000W.

So $615 for base system, + $3900 for cards +$150 for another PSU

**= $4665.**

6x 800Mhash =

**4800Mhash.**

**That's $1.0289Mhash/$1 for a 6x 6990 system.**

I'm not going to write it up but a 6x 5970 system would get

*AROUND*the same Mhash and cost

*AROUND*the same.

For the $4665 price of the 6990 system I could buy 3 of the 5850 systems. Instead of $4665 for 4800Mhash I would pay $4545 for 6300Mhash.

------------------------

I'm just having some fun here theorizing stuff. I didn't hunt around too much for prices but went with averages. I'm taking into account moderate to heavy overclocking on all of the cards, and went with rough (though I believe they would prove accurate with more research) power calculations. I already stated I left out electricity costs and I'm not factoring into account profit at all, that's why I gave all values in Mhash or Mhash/$1. So far 1.386Mhash/$1 is the best I can come up with.

Feel free to comment and critique. Just having some fun here.