I got no data to prove my point but i went with 2 seperate non-raid SSD's.

1 for windows/programfiles/anything else that runs in the background
1 for wowfolder (and the spare room for CoD:MW2 and other new games i play frequently)

this allows the entire 3GB/s bandwith passtrough to be free for wow data without any sudden windows service starting up and blocking it. I also tend to browse websites and play winamp or a video while leveling or grinding, which again dont clog up the bandwith and seektimes of the wow disk.

Raid setup would indeed mean higher read/write speeds but i dont know what the effect of windows and stuff on it makes in term of loading speed ingame.