I would love to have gone with a 500 gal setup but this will be an upstairs tank.
Currently my 90 gal with 30 gal sump is filling the spot and an interesting fact is that it is running perpendicular to the floor joists downstairs. So realistically the weight is being taken up my two joists.
I do have a new 2 year old house and the joists are the new engineered style. There has been no sagging or any issues whatsoever so far
I realize that they're are mixed feelings about the logic behind this but hey, as long as I don't notice any sagging and the tank doesn't tear through the floor I'm okay with the risk.
Additionally I feel that having a much shallower tank with a larger base footprint will help to disperse the weight more evenly.
So for any of you scared about running 2nd floor tanks. Here's an example of 120 gal sitting on two joists