We are looking for a combine to replace our 1440. We are running a 6 row 30" corn head and a 16.5 flex head but would like to step up to a 20ft. Corn yields are 100-150bpa and small grains, oats and wheat are 50's. How do the 1640's compare to the 1460 and 1660 combines. I would also entertain a 1480 or 1680 if I could keep them full. Any pros or cons for a specific model? Are the combines that don't run beans any better than the ones that only run small grains?