Thanks again to JimJ740.
There will be a thread at MR, but also feel free to post results here.
I have tried in both cMP 5,1 in a PCIE slot, and via TB in a 6,1 nMP.
It's faster in 5,1, by the way. But a hack with PCIE 3 should show some nice numbers. And if the Hack were to be based on a board with NVMe support via EFI, may even boot from it.