Flying geese (traditionally) are basically rectangles where the width is twice the height measurement.
Are those panel measurements above FINISHED or UNFINISHED?
Are you shooting for some final quilt size?
How big is the middle border going to be?
I would probably start looking at FG that are 5" x 2.5" FINISHED.
You could work that extra 1/2" in easily.
Anything wider/larger might not look right for that size panel.
Do you have a picture of it?