With due deference to speed (4)
I believe the answer is:
pace
I believe this clue is a double definition.
'with due deference to' is the first definition.
(Latin term meaning 'with due respect to')
'speed' is the second definition.
(pace is a kind of speed)
(Other definitions for pace that I've seen before include "Part of step" , "Step or tempo" , "a certain distance" , "Gait" , "With due respect" .)