IO Crest SI-PEX40057 4 Port SATA III PCIe 2.0 X2 Hyper Duo Raid Controller Card (4-port Marvell 88SE9230) works on my Mac Pro (2009) MacPro4,1 with macOS Sierra 10.12. No drivers needed. Bootable.
The Marvell 88SE9230 controller uses PCIe 2.0 x2 (5Gbps x 2 lanes = 10Gbps). In theory, you get up to 6Gbps using one SATA III device, you only get up to 5Gbps (10Gbps / 2 ports = 5Gbps) if you access two SATA III devices at the same time.
I actually recommend [[ASIN:B00WUZPMHE OWC Accelsior S PCIe to 2.5" 6Gb/s SATA SSD Host Adapter]] which provides a full SATA III 6Gbps bandwidth (PCIe 2.0 x2) and a place to mount your 2.5" SSD.
Pros:
• Plug and Play. No drivers needed.
• Bootable.
• Better than the built-in SATA II (3Gbps). SATA II: 285MB/s read, 232MB/s write. ==> SATA III (6Gbps): 540MB/s read, 381MB/s write. Tested with my Crucial MX100 512GB SSD (spec: 550MB/s read, 500MB/s write).
Cons:
• You need to find a way to mount your SATA III device somewhere. I used [[ASIN:B00SQ64PG0 Kingwin KW-PCI2H25 2 Bay PCIe Frame]] to mount two SATA III SSD devices. And you will need SATA III cables and SATA power cables...
• It has four SATA III ports but you only get up to 2.5Gbps if you access four SATA III devices at the same time (10Gbps / 4 ports = 2.5Gbps) which is slower than the built-in SATA II (3Gbps) bays.
• The storage icon in Finder shows up as an orange "external" device.
Note:
• The device (and the controller) shows up under "Generic AHCI Controller" in the SATA/SATA Express section of System Information.