I've noticed, when trying to copy TM-backups to a new drive, that mac's usb can't hold reliable connection for days.
TB is likely more robust, since there is no Apple's crappy usb driver involved.
So, not for speed, but for reliability.
This might be one solution, but these are getting very rare:
✔ Preisvergleich für SanDisk Professional ev All Terrain Case ATC, IP66, Thunderbolt 2 ✔ Produktinfo ⇒ Anschluss intern: 1x SATA • Formfaktor: SATA • Anschlüsse extern: 1x Thunderbolt 2 (20Gb/s, Stecker via f… ✔ Externe Gehäuse ✔ Testberichte ✔ Günstig kaufen
geizhals.eu
As well then, reliable connection to external drive from a mac is also getting rare...