Is there any internal differences between the 9660STS and 9760STS? I know there is only a HP and hopper difference on the '50STS's, and there is a difference in the clean grain loading systems on the '70STS's. But what about the '60's? Also, I've heard that the '06 and '07 year models were better machines than the earlier ones. True? Might be looking to upgrade to a xx60 in the near future. Thanx in advance for any comments.