if it were my house and I didn't need the crawl space, I'd go higher. We gutted the top floor of our mansard but kept the ceilings the original height (8.5') because we installed AC and needed the "attic" for the ductwork.

If additional room is easily available, even if it's straight up, you're usually best going for it. Even a foot of extra ceiling height makes a room looks much larger and with interesting walls like gables or a mansard, it would be more dramatic. Harder to wall in, yes.........heat, yea. But most of us who live in large, old houses knew that when we bought them. LOL.