I presume it would more than be fine; thunderbolt should theoratically give you the best speeds of current interfaces (esata, USB3, TB), though you’re obviously stil limited to the top speed of the drive itself.
I’ve been using esata G-tech drives and drive speeds have never been an issue; my cpu runs out before anything else does!
Just a quick question; I’m about to spring for an iMac 5k but was curious whether you have tried running it yet at full 5k resolution?
By default the imac is limited to 4k resolution, but you can switch to the maximum display size by either option clicking the ‘scaled’ option in Display Preferences or using a third party app like Quickres.
If you have ran it at 5k, would you mind posting a full size screenshot of the arrange window (with the vst dock open?); I’m just curious to see how much screen real estate you get on the full 5k setting…