The Thunderbolt2 drives will run faster. BUT! I do not know how big of a difference it will make. I have been working with raw R3D files and its no speed issues on Thunderbolt1 as far as I’m concerned. I must address that my projects are never more than 10 minutes long, and usually its a single timeline.
I would say it depends on what you are working with. If you are working with huge file sizes, multicam, and so on, Thunderbolt2 might be a big difference.
If you are more into smaller projects like promotial videos, corporate stuff and music videos I would guess Thunderbolt1 will be good enough. Its been working like a charm for me at least!