That's right. There is no generic upper limit. You have to know your floor, how it is supported, how the tank will be positioned. Across multiple floor joists(not along two) and along support wall is best.
Research the architecture BEFORE the tank goes through. It might not really go through. But might warp and sink the whole floor and walls a little bit...and it might just drop through. But I've never heard of the big disaster happening.
But if the floor moves a little, and the tank twists...crack!