I've had a lot of conversations with various folks on this forum on this topic and I think the best approach is to use a smaller number of fast drives with your WoW clients juntioned into the same install. On my new rig I am putting all of the OS and files on one Raptor 150gb 10K and all of my WoW clients juntioned on another Raptor 150gb 10K. When the Velociraptors come out later in the year I might split up the game files further but who knows.