According to what I have been told, and my experience in my youth, you can figure one acre per 8 hour day with one team. Wealthy farmers had more than one team, and could plow with one, while the other rested, then switch back to the first team, to get more plowing done. Farmers that really did well financially could buy a sulky plow, and it wouldn't be so tiring on the farmer, they could also afford more horses for the hitch. We used mostly hillside walking plows, out at my Great Grandfathers farm, he had one team, we would talk to the neighbor,'across the fence' while the horses rested. It is important to rest horses, to make sure they get water, and extra feed when they work hard. You can get more work out of mules, but they know when their day is done, and will go to the barn, with or without the plow.