Rate of climb/descend is perfectly legal under procedural.
But, in my 12 years of experience I have gotten into trouble many times using this. So much so that our sector has been temporarily banned from using this seperation due to a "recent reduction of sepration".
Problem is that there is no way to monitor this except through frequent position reports, which defeats the purpose a little. If its alot of talking you wanna do, then just step-climb/descend the guys right from the start.
What is the opinion of other procedural sectors on this?