SOME SSD read times are faster than a HD. The SATA or IDE doesn't really matter much. People confuse bandwidth with practical throughput. A hard drive will push ~40 MB per second. A SSD can push 60 or 70 in some cases, though writing will be slower. The SSD will have far better access times than a hard drive. All told, a SSD > hard drives for WoW.

All told, a SSD will be better but in practice, the difference unless you had 5 SSDs and enough bandwidth (meaning multiple SATA channels) is going to be fairly slight for a fairly hefty (as of 2008) cost versus a single hard drive.