Anyone here using a kanex thunderbolt to usb 3 + ethernet adapter. I have a mid 2011 iMac with only usb 2 so got the above adapter to add usb3. I've attached a Sammy 850 evo 250Gb to it via a sabrent usb3 to sata adapter (same drive as I've added internally). Running Aja system test and black magic I'm only getting 355MB/s read and write, from external yet get approx 500MB/s from the internal drive. Should there be this much difference between the 2 interfaces, using identical drives?