I don't think there is any loss. The rear panel is just that, a fixed glass panel in place of the steel. The front sunroof slides back over it, and there is a power cloth cover going over both.

 

I don't think that any is lost. This isn't an X6 or a ZDX, where the roofline slopes down, making like rough on tall backseat passengers. There's plenty of room back there.

 

The difference is negligible, but the front/rear headroom numbers are:

CommandView: 40.0/39.3
Single-Pane: 39.9/39.2

 

The difference is negligible, but the front/rear headroom numbers are:

CommandView: 40.0/39.3
Single-Pane: 39.9/39.2

Looks like the big sunroof actually provides "more" headroom according to these numbers.

 

Thanks everyone!