I know that!
What I was getting at is - the reason/s you are overboarding will dictate your choice of materials.
I don't see how NMP can cover all bases.
In my experience 6mm cement/silica boards are only suitable for small floors free of excessive deflection.
Sorry mate, I wasn't sure if you are a pro or just a novice asking a question.
My thread (this one) has answered and helped with choosing the the right board for different situations. As far as where you cut the line for big meterage over a large floor.. i don't know.
i wouldn't go sticking matting on floor boards though.
I haven't personally come across a job big enough to pose the question of what else to use.
But faced with a 'large' floor, floor boarded throughout would still need to be strengthened, What would you do Impish?