I've got a Late 2015 iMac, 4.0ghz i7 with a 2TB Fusion drive. I purchased an external Dual drive Thunderbolt 2 enclosure, which houses a 1TB Samsung 850 EVO for booting, and a 6 TB 7200 drive for data. I'm actually fairly happy with the Thunderbolt enclosure as far as speed is concerned. I'm getting roughly speeds of 490 MB/s write and 525 MB/s read using Blackmagic. My 3.5 hard drive is getting speeds of 172 MB/s write and 165 MB/s read (strange as the write is faster than the read). These speeds are appreciably faster than my 2010 Mac Pro. Anyway... my question is that if I were to replace my internal fusion drive with the samsung SSD... would I see any more speed increase in reads and writes? Has anyone done this and posted benchmarks with Blackmagic?