I ran Umstead in 2010. Ran it pretty well, actually, in 22:35. Here's a tip that may help you.
Based upon race director Blake Norwood's wonderful guide for first-timers at Umstead (see link "How to Train For and Run Your First 100 at the Umstead 100" on the race homepage, here), I planned for a finish of 28 hours (so I overachieved a little bit!).
I made the following pace chart up in small card format, laminated it, and carried it with me to consult during the race to try to stay on pace.
I never used it. I just ran the first lap and it felt good, as did the 2nd, 3rd, 4th, etc., so I figured, why mess with success? So it remained in my pocket until I cleaned out my gear after the race.
But YOU might need it. So hit the PRINT button, laminate it, and carry it along. You may never even think about it...or, you may find it absolutely indispensable to your personal race management. The point is, use ALL the resources at your command to maximize your chances for success.
So--print it and carry it (or Blake's similar lap plan for a 23:30 finish)--it may make all the difference for you.