I always thought (ready to be corrected) that ATC expect you to fly +/-5kts of the speed given
Do you also expect to be +/- 5 NMs separated to other traffic???
Just fly the speed given!
Aircraft no. 1: 160 kts becomes 155 kts and
Aircraft no. 2: 160 kts becomes 165 kts
No. 2 is 10 kts faster, not a lot but that's 1/2 NM in 3 mins = loss of separation! If you have to space them tight
Tell us your speed (e.g. 170kts) early enough and we'll make it happen some how