Note that PCIe SSDs installed in a Mac Pro 5,1 (MP6,1 have exactly the same PCIe 2.0 limits too) are limited to ~1,500 MB/s unless installed on a PCIe switch card in slot 1 or 2 such as a HighPoint SSD7101A-1 or Amfeltec Squid that converts the Mac Pro PCIe 2.0 x16 to the PCIe 3.0 x4 needed for full throughput. More @Wikipedia
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