Sticking to one procedure is best until everyone can do it, although there are a few who now utilise the capabilities of offset flying and ground speed readouts to separate, unfortunately very few though, as its not taught or written anywhere.
In AC at Latcc, the only way of guessing a ground speed is by watching the gaps between the returns, we normally have the last 5 displayed to give a direction too. The bigger the gaps the greater the speed. Obviously no separation can be given by this, just monitoring to check that its whats expected.
Going back to the first point, when given a IAS to fly at top of descent, the other a/c behind will be given the same IAS if about 20 miles or more behind, but the closer the two are, then the second just gets a lesser speed to a) build a gap and b)account for the height difference.
I believe the difference is about 10kts GS per 2000ft for a/c flying exactly the same IAS/Mach, anyone have the correct amount???
