The biggest difference between the two is the smart phone connectivity features of the 810, otherwise they're pretty much the same. I got the 810 for the livetrack feature where I can enter email recipients in the app so when I start a ride or race they get a link and see exactly where I am on a map and my telemetry. It can also send a link to facebook or twitter. The other feature I use often is being able to upload routes on the fly from the phone to the unit. If you don't need all that go with the 800.