SCSI slow?

Hi guys, I have a question.

I am building a workstation with a combination of: PATA drives, SATA II drives, and SCSI Ultra-320.

Now, when I tested the Read / Write speed I obtained the following results in MB/sec:

PATA (IDE).................48.........43..........OK
SATA.........................62.........54..........OK
SCSI..........................28.........23..........VERY POOR

I thought there was something wrong with my onboard SCSI controller but when I tested the SCSI drives through an old 2940 Adaptec card (that provides at least 40 MB/s) I got exactly the same:

................................28.........23........It must be the drives, I thought.

But even though they are not the latest, I never thought there was ever a SCSI so slow!
Or was there? :?:

Well, that is my question. I have never had reason to test drive speeds before so I am totally unaware of the performance of these drives nor I can find them on the net. I don’t want to blame the mobo yet, so I would appreciate any suggestions.

SCSI DRIVES:

Seagate Cheetah....ST19101WC.............9 GB....Hot-swap
Compaq................BD018122C9...........18.2 GB....Hot-swap
Quantum...............Atlas 10K 3.5 series...9.1 GB

Also, the two hot-swap drives don’t work at all unless an old 50-pin CD cutter is added at the end of the array.

I guessed that may be due to the 80 to 68-pin adapter possibly being too old and thus incompatible with U320. Possible?

And if so, why would they work in conjunction with the 50-pin SCSI device and not alone?
I always added a terminator in all my tests.

I thank you all for your time.

Maz