In this video I take you through a experiment where I use a Camera to analyse the quality of a silver screen as you move away from the centre line of the cinema.
The video shows the lowering of brightness and the inconsistency of brightness. The silver screen effect needed for clean 3D also gets much worse.
This video should help you understand where the best place to sit is if seeing 3D on a silver screen.
Also See links:
The Death of Silver Screens~! Vive la France
3D Quality on Silver Screens