For NVMe - I am using the HighPoint 7101A card. You can also go with the cards
@tsialex recommended but you won't hit max speeds of the Samsung 970 Pro or Evo blades ~ over 3000 MB/s read and 2300 MB/s write. You need a NVMe PCIe card with an onboard PLX switch which the highpoint and amfeltec have. However, you will still benefit from the higher IOPs, lower cost of the card and 1600'ish read/write speeds.
The sonnet tempo card only supports booting macOS but not Windows. Does not matter how you plan to install windows, it just won't allow windows to boot with it being present in your mac pro - check sonnet's website.
For your use case and seeing that you went with dual x5680 and 64GB, I'd recommend pimping your NVMe setup >> GPU >> DISPLAY
Cheers