All I am asking Scott, is why can't you ask the pilot what his climb rate will be. Or ask him if he can give you a climb rate of 1,000ft a minute, or 2,000ft a minute. It is obvious from all the varied responses on this and previous related threads that pilots are not sure what is meant by the term "expedite". Some think it is best possible climb rate, others best comfortable climb rate, others 2,500 ft a minute. If the pilots are unsure, why use it. Either give them a crossing requirement, as you said (and you said that may not be needed for a while, well whats the harm in giving it early and letting the pilot set up to meet the requirement now rather than later), or pin them down on what rate of climb they can give you, specify that, and move on.
To the person who said anyone who doesn't use expedite, obviously doesn't work busy airspace, that is a crock. A lot of people around the world, not working London airspace, are working busy traffic, whether that is Europe, the US, Asia, or the Middle East, and just because some of us feel the term expedite is over used or misused, does not mean we are not working traffic at high levels.