I've done DK200 the last 3 years, 2016 with a 510, 2017 with an 820, and 2018 with a 1030. Got off track with the 510 once and had to backtrack a mile or 2 to get back on the course where I went off it due to me not noticing the off course prompt. 820 worked better for navigating I thought, but both had to use an external USB battery in my top tube bag to have enough to finish the race.
The 1030 is much better, love the bigger screen and longer battery life, but I had to use the Garmin external battery to have enough life to finish (had screen max brightness, no battery saving on etc). The external battery worked fine eventually, the head unit lost awareness it was there and didn't keep it charged which I found out when the low battery alert showed up. Pushing the button on the battery pack didn't help, I had to remove the battery pack then put it back on and push the button to get it to charge the head unit which it did quite quickly, plenty left at the end of the race of course. I was a little worried the battery mount etc might not be designed for the beating from the course, but it did fine. If i make it through the lottery I'll use it again this year for sure, it's the cat's meow for distances like this for me.