Windows 8 by default activated UASP mode and a 128GB Samsung SSD 840 PRO ... Read speed 407 MB / s read and 407 MB / S. In Windows 7, with the same PC and even Samsung SSD 840 128GB PRO ... Read speed 275 MB / s read and 271 MB / S. So Windows 8 better manages the UASP mode Windows 7!
If you add a PC card USB3.0 PCIe 1X, choose the right one that supports UASP and the PCIe connector on the PC motherboard is version 2.0! and preferably Windows 8 to get the maximum transfer performance!