How about power profile & repeatability?
I measured repeatability as equal rest repeats. E.g., for 30 seconds, the 1 repeat is just max 30sec power on the ride, for 2 repeats it’s max 30 on 30 off 30 on, only counting the on parts towards the average.
I think this sums up the complete picture, or maybe I’ve lost my mind. Progression levels are on here: if your FTP is 300 and your sweet spot progression level is 6, that means you can do 3x20 at sweet spot (at 90% difficulty - rated very hard), and that’s on the graph here (albeit you wouldn’t take 20 minute rests).
The graph is from my workout today, which was 5x10 sweet spot, so you can see the shelfs at 10min (and nothing special at shorter lengths).