I went from a MF 850 to a 1680 and I loved my 1680, but I don't harvest cereal grains often so straw isn't a concern for me. When I have done wheat or oats with the case rotors I have noticed the straw is very chewed up and as I recall the MF850 left really nice straw. As far as capacity I have never run a 1660, but the 1680 seemed to be much more capable at least in corn and soybeans.