If cutting costs:

-You don't need SSDs in raid. One SSD is more than enough throughput to run 5 WoWs. Run you OS on a normal hard-drive, and run WoW on a dedicated SSD.
-More RAM is better. I would try to go with 12GB if possible.
-I personally like the amount of VRAM my video card has, and it's debatable that with 5 WoWs you may want to look at VRAM vs processor speed.