Yeah, running your own pace and denying those competitive inner demons is important. It is a very good thing that you recognize that. It's tough, but it's part of the game.<br><br>
From the few images on the <a href="http://www.trailmixracemn.org/raceinfo.html" target="_blank">race website</a>, it looks like a nice woodchipped surface. The description refers to grassy trail, too. That bodes very well for the downhills being gentle on your legs. Also, the 3:15ish winning/record times referred to on the page suggest that the race is flat enough that there won't be downhills significant enough to really pound your legs to pieces. (okay, looking again, I see results all the way into 7 hours, but it can't be that hilly if anyone is running 3:15) If there is a "ski hill," though, that sounds like a dandy place to walk.<br><br>
Don't think of walking as conceding defeat. It is anything but. It most ultras, it is par for the course, and can really be a life-saver. I will walk almost anything, particularly in the first lap of a multi-loop race. It's all about doing what you need to to get to the finish. Race pace during these events has little to nothing to do with typical road-running training pace, let alone road-racing pace.<br><br>
It sounds like you have signed up for one of the few ultras that are run at marathon-type intensity. This may make the experience far more like a marathon than an ultra, particularly in the reduced number of hours you will be on the course. With three water-stops every 7ish miles and relatively flat, non-technical terrain, you should be very well supported during the run and prepared by your typical training without a lot of trail-time. Keep stretching those long runs out and find the foods that work for you. If you are planning on maintaining a pretty high level of exertion, look to liquid calorie sources that may be easier to digest.<br><br>
Relax and enjoy your long run in the park!