With a 20F your are ok for the beans. Wheat and corn, especially 90 bu wheat, get a 9500. Depends on how many acres of wheat you have, though. A 9400 will handle it, just not as fast as a 9500 with the extra 18" of walker.
Although, with a 20' head, you should be able to cut real close to 2.5 in 90 bu wheat with a 9400. I don't know about the corn, but our 9410 and the 9400 we had before it, will/would cut 70 bushel wheat with 922 at 3.5-4.0, if you don't take all the straw, just cut for the heads. That is in HRW. You did not say where you are or what wheat you are cutting.
The 414 is plenty for this machine. Has plenty of gut to handle hills and mud. If it pulls down in mud, you should not be there, because you are stuck.