You didn't listen to anything I said.
It depends on the snake, but many snakes will go off feed with larger cages even if the heating and humidity requirements are met. It does not matter if they have all their hides and everything perfect. If it's too big, it's too big and they won't eat for you.
It really depends on the animal. If they eat fine and don't act stressed in a 40 gallon, then that's fine. But if the snake is not eating, lowering the cage size often will fix the problem.
And it is pretty impossible to control the entire heated room properly not to mention keep humidity requirements.