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I've recorded >24hrs with no issues. I've had it crash fatally after less than 24hrs too. The critical factor seems to be if you're using navigation or not.
I can't recall if I've got auto power off set or not. I know the 1000 is fine when you pause and turn off the unit but can't remember if the 800 works or not, since I use the 1000 for everything except commutes nowadays. I'll have a look and see if mine replicates the auto power off file death.
800s are fine, but you need to know how the firmware breaks.
I split my routes into 200 mile segments for Tour Divide, didn't use turn by turn, but did use cuepoints for some turnings and also city limits of major towns so I could see in the cue sheet how far the next town was from my current location. Very useful in the middle of the desert to know that it's 83 miles to the next town, so you can ration water accordingly.