Add Thunderbolt to Precision 3620?

I'm considering whether to add Thunderbolt to my 3620, which does have a Thunderbolt header on the motherboard.  Can someone tell me what kind of add-on card I might need?  I'm guessing there is a PCIe card that connects to the header.  And, can you tell me what is the highest level or version of Thunderbolt supported by this motherboard?  My main reason for considering adding Thunderbolt is to connect external storage devices any opinions are welcome as to whether this is a good reason to add Thunderbolt or not.  I'm not fully committed - but I just swapped my mechanical HHDs for SATA SSDs. The improvement in performance is so impressive it's like having a new computer.  I'm thinking Thunderbolt is all I lack.