If you tell me to expedite, I'll give you the best I can for as long as I can - I've always thought that would be a fairly reasonable thing to do!
Trouble is I fly a 340 and even in the lower levels I'd give my eye teeth to get 2500fpm unless we're not going very far. (As a sustained rate anyway - you can do it while you're bleeding the speed back)
Luckily the guys behind the radar screens seem to know that - in the UK anyway.