I’ve used the 810 powered by the dynamo and cache. Only issue is when you disconnect or stop for too long its asks you if it can power off and gives to 15 seconds to cancel. Not really a big issue as it doesn’t lose the ride.
I would suggest, so you don’t lose rides is to work to a maximum of 200km for recording and for gpx tracks. As over this it works 90% of the time but do you run the risk of it crashing and losing the ride (strava!!!)
The 810 has better battery life over the 1000 (bigger screen), and does almost all the the stuff the 1000 does. The thing I don’t like about the 810 is the mini usb charging as it means you need an extra cable and that you can’t get phone notifications.