Building up on this, here I upped the number of markets from 2 to 4 after 12 minutes (scenario B aswell) so we get to 40 carts at 15 minutes. 19 minute break even, but maximum 1000 resources behind. Plus, if you defend the first one or two waves of units cost effecient, your gold income per minute is pretty much the same at 6 minutes and just gets stronger after 12 minutes.