I have a Shoei full face and a Davida puddin'. Oddly, although I'm pretty much an XL in full face helmets I came up M on the Davida. I got it much reduced as NOS somewhere or another.
Downside is that in the UK at least it is only a hat. And I've yet to give it the ultimate test.
Tried some different type Davida's recently, and found that on every model I had a different size. One model an M would fit, while on another model I needed an XL and yet another model an L fitted best so try before you buy. Davida really needs to get them sizes aligned.
I ended up buying a Premier Black Pearl open face, which I find is a really good fit without getting to tight on longer trips.
What do you mean with the ultimate test Cyclobutch? Running against a concrete wall at ever increasing speeds?

Or coming home late from the pub hoping the wife will be waiting behind the door with her biggest frying pan?