Hello [NAME] , thunderbolt 2 offers high resolution display and high performance data transfer.  Which you already have both in your T7910 so it is not worth it to upgrade. Your graphics card is capable of multi-display at very high resolutions.  Your Ultra-Speed drive is capable of very fast data transfer speed (got the info from your other post).  So the benefit of a thunderbolt 2 is not worthy in your case.
I have the GPIE cable, but not the  Thunderbolt 2 PCIE card.  As I understand it, Thunderbolt 3 requires mobo support, and the T7910 doesn't have it, so TB2 is it.   I'm happy with my machine as is (I used a 2080 Ti for graphics and use a displayport cable). The only thing I can think of where it would be useful would be if I got a TB2 hub to plug my T7910 in, and my laptop (which has a mini TB2) and then I could more easily soft-switch to my laptop.  (Is that a thing?) The main question is whether installing the PCIe card would be worth it.   It may be moot: the card has to install in a specific slot and my graphics card might obscure that slot.  But from the standpoint of a curious monkey, what are the TB2 benefits that would drive installing the card?  Thanks.
Thunderbolt 2 in T7910 worth it?