If you must have fully functioning navigation, the Garmin Edge 1030 is the way to go. I upgraded from the 520 and I couldn't be happier. The biggest downside is the price.

Besides a fully functioning cycling computer, you can allow the unit to offer up courses on the fly based on your choice of distance and elevation gain.

FYI, at present the 520 Plus is not shipping until reported bug fixes are in place. See info at DC Rainmaker.