The SIL3132 card (SATA-II, PCIe 1.0) ran at 122MB/sec.
The 88SE9128 card (SATA-III, PCIe 2.0) ran at 75MB/sec, or 35MB/sec with FIS disabled.
The 88SE9235 card runs at 195MB/sec.
My two test enclosures are:
* SIL3726 based enclosure (RSV-5S)
* 88SM9715 based enclosure (TR5M6G)
* Linux, MDADM, RAID6, sequential read, 256k blocks.
Ableton said I should go with a single SSD behind a JMS575 port multiplier to get best performance out of the 88SE9128.
I pointed out that a single drive is not the same as multiple (switching delays),
and that replacing all of my spinning disks with SSD is not a valid solution.