Infinity is about comfort. I wouldn't use utility curtailment if I only had one AC system and if I didn;t have enouhg reserve capacity wit hteh existing unit... unless it was zoned and I could make some zones unoccupied. That my eventual strategy, to add zoning downstairs.
I think you only good option it to try and make some corrections on the ductwork. We're only talking about trying to get 650-700 CFM through the ductwork quietly. That shouldn't be hard with a house your size. Something isn't right there. It's realyl a great system and I had to see it hampered by installation issues like this.