The Evocation Wizard's 14th level ability Overchannel says (in part):
When you cast a wizard spell of 5th level or lower that deals damage, you can deal maximum damage with that spell.
Bigby's Hand is a 5th level Evocation that lasts up to 1 minute with concentration. During this duration, the caster can cause one of several effects on each of her turns. Some of them cause damage, and some of them do not. The two that can cause damage are:
Clenched Fist. The hand strikes one creature or object within 5 feet of it. Make a melee spell attack for the hand using your game statistics. On a hit, the target takes 4d8 force damage.
Grasping Hand. The hand attempts to grapple a huge or smaller creature within 5 feet of it. [...] While the hand is grappling the target, you can use a bonus action to ahve the hand crush it. When you do so, the target takes bludgeoning damage equal to 2d6 + your spellcasting ability.
If the caster overchannels this spell, do these effects both do maximum damage on any turn on which the caster chooses one of them?