My color negative conversion workflow is not close to the Coolscan+Nikonscan results in terms of speed and quality and the ICE is pretty amazing. Maybe a version of AI will be able to address these issues for me but apparently not today anyway.
Maybe not for your consideration but the Coolscan 5000 & 9000 are both faster then the 4000 & 8000 specially when ICE is turned on. For instance a full res scan using ICE with the 5000 is about 55 seconds per frame and about 35 seconds without. I recall the 4000 is in a few minutes.