Here's the logic:
#4's have better knock down punch,
#6's you have more BB's
#5's is a good compremise between number of BB's & knockdown power
Still stand by the earlier post as to what patterns best ... two identical shotguns with the same choke can pattern differntly (ie 1 with 5's and the other with 6's) ... and one manufacture will pattern better in one and a different manufacture in another.
Bottom line: Use what ever patterns best in your shotgun and choke, or pray heavily to the BB gods.