I have seen 5 bu and I have seen 7 bu.  I have seen no difference.  Might be the seed lot quality more than the shape of the seed?  I don't know but what is more important, doing a really good job of planting seed at the same distance between the seed and the same density of soil above the seed or worrying about round vs flats?

Don't mean to be smart but you get my drift.

First Choice just delivered my seed and it seems to be of very good even size, density and quality, 43 lb to 49 lb seed in a 80k bag.  I hope I can plant it well.

Do some Googling and I bet you find all kinds of results on seed size.

Ed