Metal stands are a bit more precarious. Since they support the weight on four points the load is not as evenly distributed.
I couldn't say that it would be worse in your situation. More information would be needed.
What is the orientation of your tank to the floor joists below?
Is the tank on an inside wall or exterior wall?
Is the tank possibly in the middle of the floor, not against any wall (I've seen this)?
I wouldn't worry about a 90g tank causing the floor to fail. The biggest concern, IMO would be, if the weight of the tank is causing the floor to bounce and creating an unstable foundation for the tank.
swimmer