I've just recently had a good search around to try and get to the bottom of this issue.
I always thought it was better to have any optical drives on different IDE ports, as data to and from them would be slowed if they were sharing one port.
It would appear not to be so.
The overwhelming point of view is that where possible hard drives should not be on the same IDE port as an optical drive as in theory the HDD will be slowed down to the same transfer speed as the optical drive.
I even had a note with a hard drive advising not to share it with an optical drive.
So there we have it. Looks like I was wrong all those years

(Mucks is going to gain some small satisfaction from this admission, as this is an issue on which we'd previously disagreed, lol)
And the config as outlined in the first post here would seem to be correct.
As for me:
Machine one:
2 x SATA HDD in RAID 0
IDE HDD One - IDE 1 Master
IDE HDD Two - IDE 1 Slave
DVD-ROM drive - IDE 2 master
CDRW drive - IDE 2 slave
Machine Two:
2 x SATA HDD, RAID 0
IDE HDD 1 - IDE 1 Master
DVD-ROM Drive - IDE 2 Master
DVDRW Drive - IDE 2 Slave
As for my daughter's machine, I honestly can't remember how I set that up, but it works well
