Here's what I'm working on:
-2017 15" 2.8GHz Macbook Pro
-Media & Cache on a 1TB external SSD
Basically when I first got the external SSD, my edits were flying, it was good enough that I could play unrendered 4k speed-ramps at 20'000% (so long as it was only for a second tops). Now it's a few weeks later, the SSD is never more than 60% full, and it's bad to the point where freezes for a second whenever there's an unrendered hard cut between two shots.