Well, it's not just a 16 band compared to a 13 band. It's independent left and right 16 band eq. Still, thats NOT much of a difference as most would have no use for independent eq's.
Other than that the only differences are display and exterior looks.
If those are that important enough for you then go ahead. If functionality is what you're looking at then don't waste your money. The 860 is just as capable as the 880 and the 860 has higher preout voltage.