UPDATE/EDIT: If it matters, I may add on a third and/or fourth GPU to the system later. Running a 1k watt PSU in the rig right now with ample space and airflow.
Do you plan to use water cooling ? How else can you fit 4 cards in one MB ? 
I would recommend mining on Windows, of course. Unless you are going to install more than 2x5970 or 4x5870
why is windows recommended over linux?
if you do your over clocking in windows and then flash the gfx bios then all voltage settings and such works in linux as well
You don't even have to flash the bios in Linux. I'm running 5830's with underclocked mem and overclocked GPU and voltage just by using AMDOverdriveCtrl utility and even created the profile from the command prompt and applied it there in one easy step. There is NO advantage to running it on windows but there are MANY advantages to running under Linux. Sooo much more control (oh and it's faster too).