Here are some diagrams of what the proportions would be of different sized flying geese (for your center panel 35"x40").
It's a starting point for you to decide on a look you prefer.
FG 2,5x5
[ATTACH=CONFIG]256748[/ATTACH]
FG 1.25x5
[ATTACH=CONFIG]256749[/ATTACH]
FG 1.25x3
[ATTACH=CONFIG]256750[/ATTACH]