8 down
Still
preferring
bishop
to
rook,
extremely
optimistically
(2,4)
Still preferring bishop to rook, extremely optimistically (2,4)
hints
0
checks
0
hints
The definition is at the end of the clue.
How the clue works
Extremely optimistically is your definition, giving you a phrase meaning "in the most favourable interpretation." For the wordplay, take AT REST (meaning "still"), then swap out R (rook in chess notation) for B (bishop), as the clue tells you to prefer bishop to rook, and you land on AT BEST.