I do agree with
ATC Watcher on TCAS reaction vs protection. I guess the green bow must not often be in the 8000' region.
On the other hand, 8000' is a wee not enough for an emergency descent...
An empty B777 will happilly climb like an F16.
I saw once a Mirage F1 climb from runway to interception ("visual recognition", as should be said) at FL410 in less than 3 minutes (won't tell you the actual time).
And I've heard B738s bitch because I asked them for more than 100'/min in descent (due to constraints)...
No ! They're not (all) RYR : Airbuses bitch sometimes too.
To come back to the original question, I reckon we (controllers) think more often in terms of minimum rates, rather than maximum. Even though we know there is a maximum, better not ask for it and remain in reasonable numbers, if possible.
Lord Spandex Masher,
is 8000' the max we may legally ask for, or the max a pilot can technically do (eg for passengers' comfort) ?