personally i woulldnt go with anything bigger than a fifty-five on a floor other than the ground floor. unless your place is like an industrial type place like a school or office building.
one of my moms colleagues at the highschool has a 125 on the second floor of the building with no problems but like i said its a pretty sturdy indutrial type building
I think it depends too on where in the room you place it. If its across the joices instead of parallel it might work for the 75 but I wouldnt personally go 90 without doing ALOT of research.
I agree, you wont have any trouble with it as long as you place it in the right spot. Place it next to an outside wall perpendicular to the joists and there wont be any problems. People have a misconception that the higher floors are weaker, which is wrong.