HD on One
DVD-RW and DVD-ROM on second
Fast and slow shouldn't be together on same IDE.
Years ago when hard drives and optical drives worked in PIO modes where the CPU was used for all data transfer, the slower optical drives would slow the hard drive down, because the IDE port would only work at the speed of the slowest device.
It is a whole new ball game now. We have UDMA, where the CPU is not used for data transfer, so the IDE port can run at full speed for the hard drive at the same time as having a slower optical drive attached.
The result? It is quite OK to mix hard drives and optical drives on the same cable.