MG2009, unfortunately, has USB 2, not 3. Given that scenario, Thunderbolt would be the fastest way to go, by far. If budget permits, get an SSD instead of an HDD. I have two HDDs in a Thunderbolt enclosure (one clone and one Time Machine) and two SSD clones in another Thunderbolt enclosure. The difference in speed is startling. The HDD clone takes a relatively long time to boot while the two SSD clones boot almost immediately. The time to update the SSD clones is literally one-third the time that it takes to update the HDD clone.
No argument but one of the requirements specified is
so SSDs and Thunderbolt would be unnecessarily expensive overkill for that application. Most Time Machine operations are relatively small (say a few MB), take place in background, and are mostly unnoticeable. They are nothing like a clone.
If the objective is a massively fast 1 TB external boot drive and cost is not a factor then
this configured RAID 5 might be a good choice.