6 food worker = 2.2 sec harvest rate.
3 food wroker = 1.7 sec harvest rate.
Ignoring lumber return time and 6 food workers returning twice per 20 lumber.
6 food worker harvests 20 lumber in 2.2x10=22 secs.
2 3 food workers harvest 20 lumber in 1.7x10=17 secs.
In a 20 minute period, 20x60=1200 secs.
Rounding to 2 decimal places.
6 food worker, 1200/22=54.45 returns of 20 lumber. 20x54.45=1089 lumber total.
2 3 food workers, 1200/17=70.58 returns of 20 lumber. 20x70.58=1411.6 lumber total.
Multiplying for full food.
25 6 food workers after 20 mins harvest 1089x25=27225 lumber total.
25 sets of 2 3 food workers after 20 mins harvest 1411.6x25=35290 lumber total.
If you factor in 6 food champions having to return twice that gap will get longer by about 0.2 for every return they make.
Quite a big difference to be honest.
@Beekauzh I guess it's a lot more lumber than either of us thought. About 8000 wood after 20 mins.