Up here, these days, I find that ATC usually asks if I can make a specific level by a specific DME distance. I take a rough, if somewhat educated stab, based on the performance I know that I can expect from the aeroplane. But, then, I've flown the same aircraft for the past 6 years, so I'm getting the hang of it now!
Mostly, I find that I can make the climb within the constraint. This is just as well because, for damned sure, if I say "no", I'll get held down at a fuel inefficient level until the other traffic is sighted and passed. Such is life.