I've had my 800 for years now, and will concur with what gabes said about the 24 hour thing. It's let me down twice, the other time was when the calorie counter bit (?) ticked over 10,000. That made it go wibble
I've exceeded both 10k calories and 24hrs without issue in 24hr races.
The issue is navigation and has struck me 450k into a ride. The 800 also likes to not take some NewFiles. You have to double check everything you put there has uploaded to the Courses folder because it just skips some.
I use ride with GPS and if you have ever had or currently have a 'special' character in the ride title then it won't upload. Been caught out a couple of times without realising.
I've had my 800 for years now, and will concur with what gabes said about the 24 hour thing. It's let me down twice, the other time was when the calorie counter bit (?) ticked over 10,000. That made it go wibble