In general I would say you have an acceptable setup for having two hard drives and two optical drives, assuming everything is DMA enabled. However, the HP 7550i is a very old drive, and as far as I know doesn't support DMA. That means it must operate in PIO mode and is thus likely slowing down the mobile 2 GB hard drive.
I don't see any good way around this limitation though, given your setup. Ideally you would put the slow PIO device on its own channel so it doesn't affect any other drives. But you have all the slots filled, so the 7550i must share an IDE channel with at least one other drive.
Assuming that your AOpen drive is actually the CRW4850 48x12x50 drive, then I would suggest dumping the 7550i altogether. What good is a 2x2x24 drive in comparison to the 48x12x50 AOpen drive? I would say the 7550i is nothing but an anchor at this point, and would reconfigure the system to look like this:
Primary IDE channel = Quantum 30GB as master
Secondary IDE channel = Samsung 2GB as master, AOpen CRW4850 as slave
HP 7550i = trash can.
If you insist on keeping the 7550i, then I would say you probably have things set up as good as possible. At least the main hard drive and the AOpen can operate at high speed in DMA mode. And for all I know the Samsung operates only in PIO mode as well. If that is the case, then that adds additional weight to setting up the system as you have it (again, assuming you insist on keeping the 7550i).