0.85 won't be that much smaller but you will have to decide if the slight drop in colour/clarity will be noticeable, and if a better cut outweighs these factors. I think it might as the cut determines how much sparkle it has, and that is visible from across the room whereas colour/clarity will be virtually undetectable until really up close!
That said, size is important (so she said... ) and it's the 'mindclean' factor that plays on my mind!