Update to previous post........
In order to determine the optimum method of connecting a SATA III SDD to a Vista 64-bit system with SATA II controllers, a number of add-in SATA III controllers have been tested and compared with the Intel SATA II and SATA III ports. The following conclusions were made:-
1. The Marvell 88SE91xx SATA controller passes TRIM commands (in by-pass/non-RAID mode).
2. The latest Marvell driver (188.8.131.529) gives good overall performance with the Marvell 88SE91xx SATA controller, but does not pass TRIM commands.
3. The ASMedia ASM1061 produces the fastest speeds of the currently available add-in 6Gb/s SATA controllers.
4. The ASMedia ASM1061 controller passes TRIM commands.
5. Both the ASMedia driver (184.108.40.206) and the Microsoft AHCI driver (6.0.6002.18005) support TRIM commands with the ASMedia ASM1061 controller.
6. The 3Gb/s Intel controller, with the Intel RST driver, gives speeds approaching those of the ASMedia ASM1061 and ASMedia driver, especially when used for a system drive.
7. The Intel 6Gb/s SATA controller gives the best results of all.
8. Wherever possible always connect a 6Gb/s SSD to an Intel 6G/s SATA controller.
9. The Microsoft AHCI driver (6.0.6002.18005), standard with Vista 64-bit, performs very badly with random transfers, especially with queued transfers, and its use should be avoided. The Windows 7 version of this driver is different and may give better performance. Subsequent testing has shown that the Windows 8 AHCI driver (storahci) performs virtually identically to the ASMedia (220.127.116.11) driver.
10. Future add-in cards, using the new 6Gb/s Marvell 88SE92xx controller, will probably have a performance as good as the Intel PCH 6Gb/s SATA controller.
See here for the updated report, giving full results and analysis (full screen).