Used to run a F2 and a M in the field together. M could run about 1-2 MPH faster in the same crop. Both had 20 ft heads. My F2 is 77 model and has short shoe though. If your F2 is in good shape, don't think you will gain a lot. Never could get my M to provide a clean sample like F2 does. M is parked in tree row, replaced with a L3.