we could go really panto here

There is mixed feeling on these forums, I would test it to see how it works for you. I get much better results having the clients load from a single disk PROVIDED that you use junction / mlink to have all 4/5 copies of wow use one physical data directory.

I guess it depends on your disks, my wow disk is SATA 3Gb/s capable and has a 16Mb cache; as each instance requests the same data from the disk in a very narrow time frame the disk is able to supply this information from disk cache. Also as the OS sees the request for the same information it has already provided it can often respond from processor cache. When the information comes from separate disks this is not the case.

If I had multiple disks at my disposal, I would configure them in a nice fast striped set (ensuring regular backup of the data of course) and then run multiple copies of wow of that stripe (again with linked folders for Data etc)