If you can't get 5 cards to work with Win 7, try the 90 day evaluation version of Win 8.1

http://technet.microsoft.com/en-us/evalcenter/hh699156.aspx

It will auto detect all 5 cards on install, no additional drivers needed. I did this with a 5x r9 270 rig. Easiest rig i've ever setup.