Have you tried running them without the overclock? maybe it's not the overclock.

If you plan to go big (more then 5 gpu's) it is very waisteful to make rigs of 3 gpu's or less because of the space taken and the cost of the extra components. To keep it simple lets do 15 gpu's.

So you would need 5 rigs of 3 gpu's or 3 rigs of 5 gpu's.

Ill set up the cost for a rig with 5 gpu's.

68 - open case as rob has link to.
145 - mobo (http://www.newegg.com/Product/Product.aspx?Item=N82E16813130274R)  -- This is an amazing deal at the moment I highly recommend as it is usually 195.
130x5 - 5830's
30 - cpu (http://www.newegg.com/Product/Product.aspx?Item=N82E16813130274R)
10 - ram (http://www.newegg.com/Product/Product.aspx?Item=N82E16820148368)
219-psu(after rebate http://www.newegg.com/Product/Product.aspx?Item=N82E16817171055)
9 - flash drive(http://www.newegg.com/Product/Product.aspx?Item=N82E16820171398)
15*5 risers
totaling to $1,206

Now 3 gpu rig in a case.
130x3-5830's
30-cpu
10-ram
9- flash drive
127 - mobo(http://www.newegg.com/Product/Product.aspx?Item=N82E16813157207)
50 - case(http://www.newegg.com/Product/Product.aspx?Item=N82E16811119068)
110 - psu (http://www.newegg.com/Product/Product.aspx?Item=N82E16817139006)
totaling to $726

726*5   =$4356
1,206*3=$3618

That means the 3 gpu rig costs 20% more.

I'm assuming you've actually made this? I'm planning on trying this what temp do the cards get to and what temp is the room?

Ive seen pictures of ghetto rigs with 5 dollar towel/dish rack that they place the gpu's on. I'm not sure I would do this though.

When you say it reboots do you mean it blue screens then reboots? If thats the case look at the minidump file.

I'm not really sure why some one would want 9 empty chassis. I guess if they plan to expand like crazy but still that shouldn't be included in this price you should just sell that separately if a buyer doesn't want them.

As for the 6990 they are no where to be found but they aren't that spectacular of a mining card. It's ok on electricity and it definitely requires the least amount of space but its megahash per dollar committed to a full server is pretty horrible.

If we went with the cost excluding the 9 extra chassis and including your price cut we have a cost of 2,285. Assuming you get 820 megahash per card thats 1640 megahash.

1640/2285 is .71 megahash per dollar.

An efficient 5830 rig could get 1.36 megahash per dollar so it would cost about 1,205 dollars for the same speed.

2285-1205 = $1080 waisted.

If you live in an apartment or house where electricity isn't included it would still take a very long time to make up for the waisted electricity (upwards of a year maybe even longer I haven't done the calculations)

Who knows the state of bitcoins in a year or more it could be completely gone for all we know or the difficulty could sky rocket. So yes the 6990 may be impossible to find right now but that doesn't mean people should pay more for a used card.

You technically could just lay it on some cardboard or the boxes it came in so thats free. You don't need an optical drive you can just boot with a flash drive and I guess you could include 10 15 dollars to his price for the flash drive. Other then that though everything he showed was fine.

I honestly don't think that's true. Non miners could care less where the difficulty is. The reason the price dropped from 30 to its current is because of a lack of faith in its value. This is due to several hacking incidents not to a rising difficulty.

That's why if you want to buy a machine you wait till you find some deal like that Don't be impulsive and buy the first item you can.

I'm curious how you would build a rig for under 400 dollars and get 600 megahash. Considering the 5830 is at 130. I did a quick calc and I'm just a little higher then $400 for 600 megahash and that's before shipping.

You weren't very detailed with your parts but I just tried to guesstimate the cost of the machine brand new. I feel like I was extremely generous especially on the ssd.

195-mobo
60-cpu
30-ram
1600-2x6990
30-cd drive
300-ssd
240-psu
60-case
total=2,515

That's brand new. If any one buys this at 3000 they are crazy.

Thats true they do vary by a little but what you just said is a 2.5% difference. He said it crashes at 900  mhz and its a saphire. Going off your 1020 mhz example thats a 13% difference and both of his cards are doing this. It just seems a little weird to me thats all.

I'm not sure about the $130 version but I picked up the 110 around the end of June and my cards are completely stable at 1030 mhz.

I feel like its going to stabilize until some big event happens. What that event is or when it will happen I have no clue. I feel a significant event that would cause the difficulty to become unstable would be a drastic increase or decrease in the price. If the price goes to something like 30 dollars again we will see a huge difficulty increase. If some major news source writes a front page article (not saying this will happen) that puts bitcoins in good light then expect an increase.

I have the same set up and I get 329. It's just stock voltages for me.

Alright look this has been bothering me for awhile. Please stop double and triple posting. There's an edit button for a reason.

It depends on who made your card the people saying they get above 1000 mhz I believe all have saphire cards. In my experience the saphire cards can be pushed up to around 1040 on stock voltage

I highly doubt the difficulty will ever go down. As people have already stated once you have the equipment you might as well just keep going because you are still turning a profit even if its less then before.

I wouldn't be surprised though if eventually we see 1% increases in difficulty or even less. This is where we are heading at the moment and unless some major event happens why should it not go there?

Not sure if I would be willing to trust a used card from ebay for 180. I feel like the chances of the card breaking are much higher. I would need an amazing deal to make me reconsider my stance.

A couple weeks ago you could pick one up for 189 that put it basically on the same level as a 5830 at 110 in megahash and it already beat the 5830 in electricity usage. If you can pick one up at around 189 you did good.