I looked at the Compare feature on Garmin's website and it looks like there are virtually no differences between the two models. What did I miss? and Why would I want the 810 over the 800?

I will throw out why do you want either over the 510?

My understanding is the big features the 510/810 brings over the older 500/800 are the "connected" features when paired via bluetooth to your smartphone. So things like Live Tracking, live weather updates, wireless sync of your ride to Garmin Connect, etc.

The following has some good comparative info between the 810 and 800: Garmin Edge 810 In-Depth Review | DC Rainmaker

The review is really long but there's a truth-table in the summary section that is helpful: Garmin Edge 810 Summary | DC Rainmaker

To answer your question, you may not. The 810 basically adds connectivity with cell phones to support seamless live tracking via Garmin Connect. There are also a few ancillary features, such as Live Training Partner that were added.

But if you just want a nice Garmin with a touchscreen interface and navigation, the 800 will do you fine.

I had a similar decision but it was between the 510, 800, and 1000. I went with the 1000 because of the LiveTrack, auto upload, and weather updates (also I received triple reward points and this put me over for a new car rack). I still love the auto upload and the weather updates were useful on a couple of occasions but I hardly ever use LiveTrack. If those phone features are not important I would go with older models.

the 810 is an expensive upgrade (feature for feature) over the 800. it isn't worth it imho, if you wanna spend extra go for teh 1000, aside from that the 800 is a fine device, i love mine.

I got the 800 with all it's maps/features for a great deal, less than 1/2 the price of an 810. I don't use Garmin software on my laptop, and no need to have the unit talk to my Iphone, so the 800 was all I needed.

The 800 is available at Amazon for $329 without the cadence sensor or heart belt. Does anyone know if my old Edge 305 Cadence and Heart Belt will work with it?

Better deals available, you can get the full thing with sensors, strap and maps for a little more. Point your google at Heart Rate Monitors.

Yes. According to Garmin's web site, the 305 uses ANT+ sensors, which can be used with any Computer that uses ANT+, such as the Edge 800.

https://buy.garmin.com/en-US/US/into...5/prod331.html

Thanks to everyone for the input! I think I have settled on the Garmin 800 Bundle from Heart Rate Monitors!!