Have you tried RAID 10? It combines the security of RAID 1 with the speed of RAID 0. dmraid supports this RAID type.
I was wonder what experiences there are out there with using RAID-X for performance increases. I do use RAID-1 (2 disks) but am interested in attemtps to gain higher R/W performance. Do the RAID-5's etc give noticeable performace increases?