I want to see Gerard vs bankai Yamamoto.
During his fight against Kenpachi, Byakuya, Hitsugaya trio, iirc never once Gerard had been destroyed into nothingness.
Bankai Kenpachi only cut him into 2 piece, Hitsugaya froze him, Byakuya only destroyed his whole head (which actually we know will be useless, Gerard in his base form already damaged by destroying his whole head).
So the key to beat Gerard is probably damage/evaporate him into nothingness, and Yamamoto can probably do it.