I am not really sure how to size the lights. I am hoping I have enough light but only time will tell. The light appears to be intense to the eye. To get the most intense light, the tubes need to extend down as fas as possible. The farther it extends down, of coarse, the tighter the light beam. You are fortunate to be working with a hex as I think you will not require as many tubes as a long tank does. I would try to get the biggest tube u can, keeping in mind the rafter spacing (if uou do not want to modify the roof).
Easiest way to talk your wife into a new large tank...build her a new house.
Jeremy