As to the RTK working with 2wd, we have a Trimble on a 4640 and it lays up straighter rows pulling 8row bedders than neighbor with a JD system on an 8310 mfwd and 6 row bedders.   Our rows were close enough that we planted 8 and picked 6, cotton that is, which, requires you to be MUCH closer to the drill than a corn head.