What is your measured throughput rate? USB 3.0 has real throughput rates of about 450 MB/s (and not the promised 625 Mbyte/s = 5 Gbit/s). The transfer rates of the Samsung 860 are also very volatile, depending on whether you are writing, reading or what data type. I would consider anything between 300 and 450/500 MByte/s as "good". All these tests were carried out under laboratory conditions. With the IcyBox, throughput rates of "only" 260 MByte/s are reported. Does the MacBook Pro have USB 3.0 on all USB plugs? Maybe that helps, otherwise get back to me with a few more details.