|"First of all, your bios has to support the add on card."|
If you want to be able to boot from a drive connected to the PCI SATA controller card, you must be able select SCSI in the Boot Order or similar list in the bios Setup, and have SCSI listed before (above) hard drive. That's virtually always there in a retail mboard model's bios version, even for mboards made in the 90s, but it may not be there in a brand name system bios version.
If you don't need to be able to boot from a drive connected to the PCI SATA controller card, then you don't need the SCSI setting in the bios.
"Then if the drive is seen by bios as a scsi then it may or may not still be usable fully. Most drives still have a way to defeat it down a lot but to get any advantage you need a much newer system."
Windows supports a SATA drive controller by using it's legacy built in SCSI support. He is probably going to have no problem getting the card to be able to run the drive at up to the max burst speed the drive he connects supports on the same card on any system. The card's "bios" on a modern card supports recognizing any size of drive.