Sorry didn't see this thread until now.
I think you're on the money. a 3/4" inch hole will be too small to take advantage of an SDS Max. Sure it would be easy on the tool, but it would also be slower than the best SDS+ units. Having said that, I'm not sure if MAX would be slower than those two units, which are unlikely to match the 36V/54V units we tested against.
EDIT: it appears that Dewalt 20V unit has the same specs as the Flexvolt SDS+, so maybe it will!
Let us know how you get on!