[Brightcolours]

Yes it does, that's also the only way to have any kind of grid inside the viewfinder.

 

I think it's f/2.5 with standard screens and f/1.2 with special manual focusing screen, which is pretty pointless most of the time because either the lens or the mirror or the screen won't be in calibration with the image sensor, giving you back/front focus.

There is no issue reported by any 6D owner on any forum that I have seen of calibration issues with a changed Canon Eg-X screen, obican. I have no such issues with my Eg-S either, nor the standard one. Issues of that kind usually arise when people use 3rd party focus screens which originally came from different cameras.

And you are correct, with the Eg-S you can judge large aperture lenses being in focus like f1.2.