Lots of issues here.
We are back to the argument about runway capacity at LHR. Please bear in mind that we are down to minimums on the approach; if you bust your speeds we immediatly lose separation. I have been here several times and it is becoming "policy" that the one who slows down goes around, not the traffic behind.
These days the performance on final varies considerably. Compare for instance a B757 to a B773. There could be as much as 45kts difference in the Vref. At Heathrow it is becoming more common to ask for 170kts down to 4D and provided we are asked early it is not a problem. That doesn't effect capacity: bigger gap yes but higher speed, same result.
Yes, 15kts over 10 miles would be about .75nm catchup IF the lead aircraft didn't slow inside 4D but with some type combinations 4miles separtion at 10D could be less than 2 at touchdown. A Conc. is only 30kts faster down the approach than standard but we allow twice the space, typically 6 miles, and even that can get tight.
Would 160kts to 5D be a better "standard"?
Point 4
