Most efficient use of 2 raid arrays/2 seperate HDs

Hey all,

So as a Blu-ray author by profession, I have been pondering this question a lot. Our machines at work have hard drives laid out as such:

C: = 1 hard drive for OS and programs
Y: = 2 hard drives in RAID 0
Z: = 2 hard drives in RAID 0

Both Y and Z have identical hard drives for their RAIDs, and both are connected through a PCI (possibly PCI-express) RAID controller. 'Drive' from on on refers to the Y and Z RAID arrays. My question is whether it is faster and more efficient to edit data mostly on one drive, or keep going back and forth between drives?

For instance, often we run 40GB .img files through tools that edit some aspect of it, and just output another edited 40GB .img file, so we are talking about pure sustained hard drive performance. Would it be faster to have the source .img file reading from the Y: and writing the output to the Z:, as opposed to having the source and the output on the same drive? The rest of the system should be up to speed, 3.33 xeon dual core cpu but the tools we run aren't programmed for multi-core usage.

My gut tells me that it may be better for this particular system to read and write to different drives, so that you would have both physical discs of the Y drives reading, and both of the Z drives discs writing. However, for non-RAID hard drive systems, where Y and Z were single discs, would the same hold true? I feel like the OS and hard drive logic boards might know you are writing to the same single physical disc, and so might not even send it to the controller, and instead just copy it internally quickly.