6+12 PIN (Macbook Air 2011 - A1370) SSD transfer speeds issues

I upgraded my MacBook Air 2011 (A1370) to a Crucial MX500 SATA SSD with better speeds and would like to give the original APPLE TS128C (128gb) a second life. I have tried a basic enclosure that does the Apple 6+12 PIN => USB 2/3 conversion but the read speed doesn't go above 50 mb /s. I figure there are 2 ways to looking at this: - Either find and use a better USB3 case that does the Apple 6+12 PIN => USB 2/3 conversion with a better chipset, in which case I need recommendations? - use a Apple 6+12 PIN => SATA 3 conversion board and then use a classic SATA 3 to USB 3 enclosure but I don't know if that will work? So what do I need to look out for to get good transfer speeds?