Hi everyone.  Newbie here. I'm in the same boat.
I want to get a decent rig myself already with a good ROI.  I do pay for electricity so that's key.

Thanks in advance.

Hey guys, looking good!  

Here's my modest machine, I use it for work and gaming as well as mining. My office is right next to the living room, and obnoxious whirring fans got the big thumbs-down from the wife. So I watercooled it.







Cards are 2x7990s, radiators are 1x120, 1x240 and 1x140. Case is a Lian Li midtower. The radiator fan shroud looks nice, but it does restrict the fans a bit. The mobo is an older model, and I had big stability issues getting it to run with 4 GPUs. I threw an EVGA power boost in the 1xPCIE slot and bingo, works perfectly. Individual GPUs are undervolted to 1.150, 1.145, 1.160 and 1.110v respectively. These are the lowest stable values I have found and it saves a few hundred watts at the wall compared to stock 1.2v.

Speaking of power, here we are pulling 1300w...



You'll notice my PSU is a Corsair HX1000. Funny thing about this power supply, it's actually a 1500w unit in disguise, but Corsair couldn't label it as such or else they'd lose the efficiency rating. I grabbed it for $70 from another forum member last year and have had no stability problems pulling 700w+ from each rail. The fan doesn't even spin up all the way pulling 1300w. I had it at 1450w for awhile before I undervolted the cards. The thing is a beast.

And the results are about 3.1Mh give or take, each core running @ 1100/1500. GPU0 runs the desktop, so it hashes a bit lower when the computer is in use. To game, I simply shut off one (or two). Interesting story about the VRM temps, when using the stock thermal pads on the EK waterblocks they were shooting up to 80 degrees or more. I replaced them with Fujipoly thermal pads and they literally dropped 20 degrees. I totally recommend them.

Happy (and safe) mining everyone!

I am running a Vapor-X. The maximum I can get out are 760 kh/s at 1095 MHz core and 1500 MHz mem, drawing 266 watt out of the wall.
As energy costs a fortune in my country I have optimized it not for max hashing but for the best energy efficiency. I am running the card at 975 MHz core and 1250 MHz mem. In this setup I get 680 kh/s and the card draws 190 watt.

I really like the H81, i just wish i was able to get all non/powered.  After multiple testing I was able to get 5 cards running good with non-powered risers.  One card no matter what with non-powered one seems to run around 80khs (all cards are 280x's) so that is horrible.   As soon as parts get here Monday splitting between two motherboards.  Using two corsair RM 1000's as PSU's.  

Windows 8.1, all latest drivers.