I had to replace all the tiles on a bit of my house this summer & used exactly that insulation - you can feel the difference already.
Thanks James. We are starting conversions up top in the spring and whilst a bit higher headroom looks just like your middle picture.
It's good to know that there are French public finances available for this, and more are coming. It's a bit hard to find out all about them, but we found three different ones, and out of about 14 000 euro investment on fibre de bois loft and eaves insulation, and changing the heater from a 70s oil-burner to a new oil-condenser installation (you have to do two types of energy-related works to qualify for the finances) we got over 7 000 euros back, so it's well worth it.
This is a good place to start :
I have this or something very similar in my loft. I went up into the loft whilst installing my wood burning stove, and found that it wasn't too thick in places. It was done 10 years ago. I wonder if it needs 'topping up' occasionally.