You should never be at max rage, that would potentially waste rage which is for all intended purposes stored damage. At 90 rage, a bloodthirst crit would mean reaching 110 rage which leaves 10 surplus for melee attacks. If you end up at 120 when enraging, you're potentially losing rage.

The exception being when the boss is at 21/22%. Save the rage for execute phase at that point. Second pot + bloodthirst + recklessness then 2-3 execute into berserker rage into 2-3 execute = Extreme damage.