As good as possible (5)
(Other definitions for best that I've seen before include "erstwhile drummer" , "BOSOM] ?" , "Supreme" , "12 21[FOOTBALLER" , "Worst -- as good as can be" .)
(Other definitions for ideal that I've seen before include "Dream" , "Perfect but perhaps unlikely to become reality" , "faultless" , "fine" , "Model of ethical behaviour" .)