Grayout has a 90g acrylic but I think he is looking to sell it as a tank w/stand rather than as a sump. Check out his thread - Tank Teardown
David, do you really need the extra height/water from a 90? They are the same footprint as the 75, just taller. It would seem the taller tank would make it harder to get in and out of the sump tank to do anything with it?
I would stick with the 75. You would need to make a tall skimmer stand for your MSX250. Would be hard to get into the 90.