Topped out (6)
I believe the answer is:
peaked
'topped out' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for peaked that I've seen before include "Reached the height of one's powers" , "Reached highest point, say of fitness" , "Reached one's greatest capacity" , "levelled out" , "Reached maximum intensity" .)