You should spend a few minutes thinking about YOUR process. Pencil and paper can help diagram work/data flow and highlight any conflicts.

I like to keep my OS by itself so it doesn't fragment and slow down the load or swap functions. How you allocate the other channels depends upon your process. Do you want to render to a separate drive, prepare DVD files on a separate drive? I added another IDE controller to keep extra drives as primary, but the PCI bus is still the bottleneck. I capture to one drive, render to another, then prepare DVDs back to the first. That minimizes head movement (by having a physical drive perform a single function with a single set of files) and minimizes command latency (primary waiting for secondary to get off the channel). So you don't want your render drive and prepare (for DVD) drive on the same channel. Then you don't want your prepare drive and DVD burner on the same channel. Your capture and burner could go together because you're problem not going to be burning while you're capturing. What are the savings? Can't say but from a design stand point I think it's better.

There may be other tweaks or issues that folks can chime in on. I wrote code for disk controllers and disk drives in a past life and these are the things I looked for and found solutions to.