At my PCIe x1 Steckkkarte with NEC / Renesas controller SSD via USB 3.0 so when reading measured 250 MByte / s. This is the maximum, so expect the chipset (P55) to the PCIe lanes of the CPU.
What faster I have not, but I'm assuming the built of Sharkoon Controller (not SSD) is also sufficient for the hard disks of the next two years even.
With three different drives (1xHDD, 2xSSD) no compatibility problems arose.
