I have a X5DA8 and X5DP8 motherboard, both have Adaptec 7902 B0 U320 SCSI. After installing RedHat 8.0 with version 1.3.0 driver, the dmesg shows that the U320 hard drives cannot run at 320MB/s.
This is the driver problem, please upgrade to the new version 1.3.9 driver. You should then be able to see the dmesg showing 320.00MB/s.