@bigsky: What is your objective here? How is being a dick helping the original poster, who is a prospective EV owner trying to learn more about the practicalities of charging?
Stop digging your hole and being hopelessly fixated in 40% or 80%.
Whether you charge to 20%, 30%, 50%, 70%, 80.53769%, or 100%, it will take less time [charge a Rivian] with a higher capacity dispenser than it does with a lower one. Settled law, not up for debate. Sorry.
To the OP, I bet you weren't expecting all that. Your questions were pretty much answered I think. Your first couple of long trips will be learning experiences and you will probably waste time at chargers on those trips. I haven't done a ton of multi-charge trips but it really isn't difficult. It got much easier with Tesla chargers.