I would certainly hate to be limited to one shot size & one load. "IF" two sizes & loads were allowed & lead were legal for all I could make a pretty good case for an ounce of #7 & 1 oz of #5. Add a 3rd size & I would go up to #3 for pass shooting geese. Do you note the pattern, I like the Odd numbers rather than the evens but would pick #8 over #9. for smaller than #7. As #7 is not aways easy to come by I have usually relied on #7 instead.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra