Surpass old cubicle, so to speak (5)
I believe the answer is:
excel
'surpass' is the definition.
(synonyms)
'old cubicle so to speak' is the wordplay.
'old' becomes 'ex' (prefix meaning former or onetime).
'cubicle' becomes 'cell' (synonyms).
'so to speak' shows a homophone (sound like).
'cell' sounds like 'cel'.
'ex'+'cel'='EXCEL'
(Other definitions for excel that I've seen before include "Do particularly well" , "Do brilliantly" , "Outdo" , "Outrival" , "Be exceptionally good (at a subject)" .)