For speed, use them in top, perhaps (5)
I believe the answer is:
tempo
'for speed' is the definition.
(I've seen this in another clue)
'them in top perhaps' is the wordplay.
'them' becomes 'em' (abbreviation).
'in' means one lot of letters goes inside another.
'perhaps' indicates an anagram.
'top' anagrammed gives 'tpo'.
'em' going into 'tpo' is 'TEMPO'.
'use' acts as a link.
This may not be right. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for tempo that I've seen before include "Pace of a piece of music" , "Speed at which a musical composition is to be played" , "Musical time" , "Pace - pacing" , "Rhythm, metre" .)