The 85 is a much more powerful calculator, obviously. It allowed for more equations to be graphed at a time, and more importantly, it could handle assembly language.
Benefits Over TI-83+
While the 85 is older than the newer calculators (designed in 1992), it has a few features that the 83+ doesn't have. One of those is the "soft keys" that are below the screen. They allow for easier navigation. The second feature is the equation solver. Unlike the 83/84 models, the 85 can have the equation in the form of "3A=9" instead of the equation needing to be equal to 0.