My stock voltage 5830@ 1020MHz does 327MH/s under CGminer in linux. 981+ ~650 for the 7970 will get you 1.5-1.7.
For putting the 5830s in a new rig, assuming you can't find used parts, you'll perhaps want to look at something like this:
http://www.newegg.com/Product/Product.aspx?Item=N82E16813131813with a pcie 1x to 16x extension cable and 2 16x to 16x extension cables. The advantage of getting an AMD APU system is you get those extra few MH/s from the integrated GPU and bumps you up to just over 1GH/s. Don't need much pcie bandwidth. Don't need more than 2GB of ram. Don't cheap out on the PSU.
See here for a lot of network data that can help with how much you will make:
https://docs.google.com/spreadsheet/ccc?key=0AlfvS-7vLyHjdGIyUjdDSFJsT2s5TWdIX3hNcWF5ckE^the difficulty should change in just under 5 days.
This is my favourite calculator:
http://98.201.170.173:81/btc_calc.phpYou can set your system up with BAMT and leave it running. Easy to configure, easy to check stats. I use CGminer under it with my 5830.
http://bamter.org/The only thing I have found is if I shut the system down, I have to reflash the usb drive and reconfigure because it seems to corrupt itself. But that doesn't take too long and overclocking with CGminer couldn't be easier.