actually "mixing" hard drives and optical drives does the exact opposite of what you said slycrel.
By putting the two hard drives on two seperate IDE channels, you allow each drive to have a max amount of the IDE channel's bandwith. Therefore, whenever you have to transfer data from one drive to another, or when programs are being accessed from both drives, you are not bogging down one IDE channel with both hard drives. It is a much better option to put one hard drive and one optical drive on an IDE channel whenever possible.
As far as four drives using too much juice, I don't think that carries much weight. For a normal system, you can run 4 drives and everything else on a 350watt PSU with no problems, and 350 is about the minimum these days if a system is anywhere near new. Maybe worry about that SNAAAKE if you are on an older system with a very small PSU (300w or under) but otherwise, there is no way that those drives are taking up too much power.