Right now I have a 720 that I've had for a couple of years. I was looking into upgrading the maps, since I haven't done that since I've owned the unit. As I was in Best Buy today, I saw that I could get a 740 Live for $119 on clearance from $299. That's not too much more than just buying a map upgrade. Considering I could use the map guarantee to upgrade the map, is it worth it to upgrade to the 740? What are the main differences between the two? Any information and advice would be greatly appreciated. Thanks!