WHAT DID WE LEARN?
Though the upcoming 2019 Mac Pro is a perfect platform for the Sonnet M.2 4x4 PCIe Card, the 'obsolete' Mac Pro tower can clearly benefit from the increased storage speed it provides.
Though the PCIe 3.0 x16 slots in the 2019 Mac Pro are capable of up to 12,000 MB/s, the PCIe 2.0 x16 slots in the 2010 Mac Pro are limited to 6000MB/s. That's still fast and useful.
Also, because of the 2010 Mac Pro's PCIe bus speed limit, we observed that three striped 970 PRO modules transferred as fast as four. So that opens the door to using the fourth M.2 flash module as a separate volume. For example, you could have a single module as a boot drive running macOS Mojave and the remaining three striped (RAID 0) modules serving as a very fast read/write working project volume and/or scratch volume.
You may be tempted to purchase the less expensive flash module like the Samsung 970 EVO Plus but be advised it requires a firmware update to be compatible and reliable under macOS.
You can install the Sonnet M.2 4x4 PCIe Card in an external Thunderbolt 3 PCIe Expansion Box and plug it into your 'recent' Mac mini, MacBook Pro, iMac, or iMac Pro's Thunderbolt 3 port. Sonnet offers the THREE slot Echo Express III-D for that purpose. Keep in mind that you will be limited to Thunderbolt 3's 'real world' max transfer speed of around 2600MB/s.