Keeping a multi-story house cool using AC and attic fan?

[Mercula]

Youre doing almost exactly what Im doing with the similar set up but only two stories above ground. I however do not have central air and have installed multiple window units. Can I add a question to your question ? how much of the cooler air do you think descends down to the basement making the basement even cooler leaving the upstairs floors warmer? I was tempted to hang a heavy curtain or something going to the basement to See if it kept more cool air upstairs.

My living room ceiling is vaulted up to the second floor, I do have a ceiling fan hung on a drop in the living room and have noticed it most definitely keeps the temperature more consistent between the two floors with that fan running circulating between my first floor and my second-floor essentially.