It appears that despite the 160 to 4 instruction, most of us actualyl fly 160 to 4.5 to 5 ish. If that is what is actually happening, and its not messing up the flow rates, then why not just change the instruction to "160 to 5"? I bet you would get more compliance as well. Whilst most of us probably slow down between 4 and 5 to meet the stablised approach criterea, I'll bet there are some out there who say "I can't manage 160 to 4, so I'm going to completely ignore it". If you give 160 to 5 then they woud probably give it a better shot.
Also w.r.t the mode S comment earlier - what does your mode S show - my current IAS or my current selection in the MCP speed window? 'coz whats in the MCP speed window is completely irrelevent. In a 757 If I wind back the speed window at 4.5 miles, My IAS will still be 160 at 4 miles - which is what you asked me to do, but if you are monitoring what I'm setting then you will assume I've slowed down early - which I haven't.
If I wind the speed back at 5, then the IAS will start coming back somewhere between 4 and 4.5.
FWIW I always try and tell the Gatwick director if I am very light weight, for one, so he knows that I will be slowing back to <120kts, so anything fast behind me is goign to catch up damn quick in the last 4 miles, and for two, so hopefully he will realise I cannot slow up from 160 to 115 in a mile, and be stable at 1000ft.