In most cases, I don't have control over the GPX file, I'm downloading it from "MapMyRide" or some similar service, and I can't name the waypoints.

I read somewhere that the 305 has a limit on waypoints. Is this true? A 50 to 70 mile ride could easily have 200 waypoints.

Would the 605/705 be a significant improvement over the 305 in this regard? Are the maps and turn by turn directions that much better?