Certainly food for thought.

I would agree that A4 is a better size for map reading, but a board that big would be a bit of a problem.
If the map is folded so it sits on an A5 board i should still be able to read it, i'll just have to pull over more often to quickly refold it (which would be better than pulling over continually to remove map from pannier, read and then replace).

Will give some more thought.......