2 disks configured as a RAID 0 (Striped with no fault tolerance) is definitely faster than running 2 disks as a master/slave configuration.
Personally, I've got a RAID 1 (Mirroring) because it reduces my need for backups, but it all depends on what you want.
BTW, the mirror is for my backup server. I am totally aware that it is the worst config performance wise. My main workstation is a single hard disk machine.
Note to self: Whew, there's plenty of time to look like a fool on tech threads, no need to do so within the first 10 posts.