How full is the disk?

Current WoW for me is pushing 30GB, not sure how much Win 7 takes up, but you might be getting close to filling up the disk. I know the vertexes (vertices? :P) have a certain amount reserved for disk management which is outside of the 60GB capcity (4GB maybe?) but there can definitely be an issue with degraded performance on fuller SSDs.

If this is the case, two options I can think of. Get another ssd and raid them. Put your OS back on your platter drive and WoW only on the SSD and see if there is a difference.