Tks 120.4 & Gonzo,
My absolute minimum is 5 NM spacing (mainly for local pilots) as our 2 rapid exits not at optimum locations. If preceding medium arrival, we are comfortable with 6-7 NM spacing but preceding heavy we are comfortable with 7-8 spacing. Of course, speed of following arrival is another major factor.
We have not implement land/depart after ... , so we are not that much off from one of the busiest airport.