I had a RAID (mirrored) setup, but I had the drives split into two individual drives - C: and CS3 scratch disk. Works well.
That is stupid. There is zero speed advantage to having your work drive and scratch drive on the same physical disk or RAID array. The only way you gain any speed advantage is if they are completely separate physical devices, either separate arrays or single drive. And having separate partitions wastes disk space. Putting multiple partitions on a single drive is a holdover from DOS days when drives were bigger than the original FAT filesystem allowed. Now that file systems support exabyte-sized drives, there is no speed or any other advantage whatsoever in putting more than one partition on a single drive or RAID array.