one of my side business is in retail. i only use this to pay for my yacht and my french girlfriend who lives in ontario.
anyways, the rule of thumb is if it's a small product that sells quickly, the smaller the markup. think of it as more of a $:real estate it takes up:time to sell ratio.
so the profit would be about the same on 100 1-lb packages of protein as it would on 10-10 lb bags. even though you might sell 100 1-lb packages faster, the cost of labor would be ten times more than selling 10-10lb bags (assuming customer pays for other shipping costs).
Unless you're Ross Erstling, who just takes a dick in the ass and calls it a day.