My hunch is that the biggest difference you'll find with flour is freshness. If you could find grain milled yesterday (or today!), I bet it would have a much better taste, even if it was from the least expensive brand. So, possiblepossibly outside the scope of your question, but, an airtight container for flour is definitely a good idea, as is testing out a grain mill or finding a bakery that has fresh flour, if you're really interested in the secrets of wheat.