Someone must be able to confirm if I can boot into bootcamp on either;
1) Accelsior card
2) Sonnet Tempo Pro card (w. 2 SSDs)
...installed in the Sonnet Echo Express III-D?
Sonnet says the Echo Express III-D enclosure is not PC compatible, but does that mean it will not work either for bootcamped Windows when connected to a nMP via TB2?
Please help me before I lay down another USD1K on the enclosure...
Sorry, I don't know the full answer to your questions above and I don't have a new MacPro either. However ...
I can give you some of my experiences with my old MacPro 5,1 and the Sonnet Tempo Pro Dual SSD PCIe card. I currently have a pair of 512GB SSDs in RAID-0 as my boot OS X drive on the Tempo Pro card and it works great. I have tried
without success to boot Windows from this card, either alone on a single SSD, or along with OS X with separate SSDs. I think in another thread someone posted that Sonnet Technical Support confirmed that the Tempo Pro wouldn't boot Windows in a Mac Pro. Thus, I would be very surprised if this card booted Windows any better over a Thunderbolt interface, especially in an enclosure that is advertised as being non-Windows compatible. I have my Windows boot SSD on a separate Velocity Solo x2 PCIe card.
I have also tried a variety of external Thunderbolt drive enclosures to find a
bootable Windows solution for my iMac and MacMini. Most of the Thunderbolt enclosures I have tried were unable to boot Windows ... but several did not claim any Windows compatibility anyway. The Thunderbolt enclosures I
did have success with and am currently using to boot Windows are the LaCie "Rugged" and the Seagate Thunderbolt Adapter normally used with their "Backup Plus and GoFlex" disk drives. I use the bus powered Seagate adapters, but others have posted that the powered adapters work as well (which might be a better choice if you are using large/fast SSDs >256GB due to bus power issues). You can find the drive shells for these on eBay to make a finished look to the installation.
I don't know if any of this experience is applicable to the new Mac Pro in your system, but I hope it is useful information for you.
Good luck and please post what you try and the results you experience.
-howard