I have used the 305 for a year and just upgraded to a refurb 705 mainly because I needed power recording that the 305 didn't provide. I always loaded crs files into the 305 and followed the little line on the screen because I don't like to do the same routes over and over, and it worked well unless there was a fork in the road or a lot of streets close together; then I tended to make mistakes and have to backtrack a bit when it told me I was off course. BUT after my first ride with the 705 I found out why it's an order of magnitude better: I loaded a gpx file of a completely unknown 70mi route I found on garmin connect and headed out. I was able to keep a screen with 8 data fields up while I rode and when I was approaching a turn the 705 beeped and changed the display to show where I needed to turn AND what the street name was, just like a "real" gps. When I got closer it double beeped and showed me again. No more constant staring at a screen with only a couple data points and a little line drawn on nothingness! You can download completely free routable maps from the opensteetmap website and have all the maps you need for the price of a 4gig micro-mini-super-tiny SD card.

If you usually do the same routes and know your way around then the 305 is great. If you like to explore or simply change things up then the 705 is definately worth the $$$