StreamingDir subfolders on different drives?

Running WSM 4.0.1, single standalone server (Win Server 2008), serving 2 XP-based, volatile cache OS images to two device groups (17 clients in Group 1, 8 clients in Group 2).

Our IT department is looking at configuring a RAID 5 array in our WSM server. I have read in the Sizing/Planning guide that while a RAID setup can improve read speeds, it can negatively impact speeds when writing.

My question: is it possible to locate the 'osimages' folder on the RAID drive, and locate the 'writecache' folder on a non-RAID drive? Or, do both folders have to be located in the same 'StreamingDir' folder?

If it isn't possible to 'split' the folders, should we avoid implementing a RAID array, and just stick with having the whole StreamingDir folder on a non-RAID drive?