if you are looking for performance, i'm not sure you'll see much of a gain by spreading files across the same drive. you still have the same bottleneck... a single read head on the drive

for performance, i would generally consider multiple drives and spread your wow folders across them.
this would give you multiple read heads focused on pulling the files, which would radically improve the read times.

i had posted a thread to start discussing such a solution here:
5x wow box spec (current: $1,639 +s/h+tax)

general wisdom seems to lean away from multiple drives today... with the SATA drives being enough.
i have not tried to compare yet... i'm still spec'ing. i figured you'd like to check out the info

oh, and welcome to the boards, Sarduci! nice first post