The HP in a S670 is inbetween a 9770 and 9870, the overall machine is basically the same as the 9870. Difference is basically only cosmetic and few extra options. The S680 is bigger than the 9870, we figured in the 15-25% range in 50 bu canola. The cleaning capacity is larger and is improved, going 20% faster in 50 bu canola and throwing out less than our 9870. S680 has more options than the S670, larger hopper than folds, rethresher versus returns back into the rotor, etc. If you are looking for a bit more capacity but basically same machine get a S670, if you want step up then move into a S680...only my opinion though.