In my opinion this "160kt till 4" thing is not just about noise, priority is the squencing of the aircrafts. The crowded airports like LHR they keep 2.5 miles between the aircrafts on final and they need precise speeds to use the airport at maximum.
And they are ridicilously strict about this thing that , there was a report i saw, saying we crossed 4 miles at 159 kt
Yes, that's clearly the case at LHR. The difference between, say, 160kt and 150kt is 3 extra landings per hour, which is a huge difference when you're operating at 99% of capacity for much of the day.