HI Dave,
I'm in a similar situation, my tank is in the basement and the ceiling above the tank was dropped downed to 7' also. My tank is 38" off the floor, tank height is 28 inches with an opening for access of 10" and an 8" gap to the ceiling.
Like others have said, 40 inches is good, plus is depends on your height also.
My bar stools are adjustable so everyone is pleased
Are you having an opening from the front to access the tank? From the hobbyists that I know who have in-wall's without an access door they really regret it, especially on deep(F-B) tanks.
Is there a build thread yet?