I have my Samsung 840 Pro in my Mac Pro 5,1 (via PCIe Velocity x2)that I want to use once I get my nMP. What is the best method to use it as a editing/scratch disk while getting full speed out of it?
Buy a used rugged 1tb LaCie thunderbolt drive from their outlet store and exchange their 1tb spinner out for your 840 Evo.
UK example:
LaCie Rugged USB 3.0 Thunderbolt - 1TB Reconditioned
https://www.lacie.com/uk/products/clearance/products/?id=10007
TB2 not necessary as TB1 is more than enough bandwidth for a SATA3 SSD.
That looks like the old model, without the integrated thunderbolt cable.
Do you know if they upgraded the controller in the new version, or the old version will give the same speeds once upgraded with a current SSD?
I have no idea - all I do know is they are relatively cheap, easy to take apart and refit your own SSD inside and as the maximum speed of the 840 Pro is less than Thunderbolt 1 speed it runs as fast as it can go.
TB2 is not necessary for any single SATA3 SSD, multiple on raid that's a different story.