Most favourable (7)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">most favourable</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for optimum that I've seen before include "Most favourable point" , "Most appropriate" , "Best, most favourable" , "model" , "Best (result)" .)
(Other definitions for optimal that I've seen before include "Am pilot being at best" , "Most favouring" , "top, surprisingly" , "Plot aim (anag) - most favourable" , "Best possible" .)