WHAT DID WE LEARN?
The 2017 iMac Pro's PCIe flash storage is fast but, with the right combination of flash blade and PCIe M.2 carrier board, the 2010 Mac Pro can compete. (NOTE: The iMac Pro had the fastest WRITE speed but was beat by three other examples on READ speed.)
After posting this we obtained test results for the iMac Pro with 4TB PCIe flash storage. It measured essentially the same read/write speeds as the 1TB. So ordering the optional flash storage gives you greater capacity but not faster transfer speeds.
Why two different flash blades for 2013 Mac Pro? When Apple first shipped the Mac Pro "Turbo Tube" in early 2014, it shipped with a PCIe-based flash blade that topped out at 1170MB/s. A few years later, there was a 'silent upgrade' to a flash blade capable of much faster large sequential transfer speeds. However, the 2013 Mac Pro 'hits the wall' at 1500MB/s internally due to the 5.0GT/s link speed and other factors.
The only way to make the 2013 Mac Pro go faster is to boot from multiple striped (RAID 0) Thunderbolt 2 drives like we did with three LaCie Little Big Disks which achieved 3740MB/s by bridging the 3 Thunderbolt 2 busses.
We included the 2.5-inch SSD installed in the 3Gbps Mac Pro tower factory drive bay to show you have far we have come from early SSD days.
Stay tuned for a report on fast external Thunderbolt 3 storage options for the iMac Pro (and other Macs with Thunderbolt 3 ports).