I can make a few suggestions. In my first 100 mile race, the Pinhoti, I estimated I could run a 16 minute pace and still finish in under 27 hours. Then I went out to Veteran's Park and tried to run a 16 minute per mile pace. I found out it is not possible for me to run that slow. I tried walking 2 minutes and running 2 minutes and was still moving at a 14 minute per mile pace. (By running I mean going as slow as I could and still have it qualify as a run.) I simply could not move at a 16 minute per mile pace. That is when I decided to try the two on two off plan. As I mentioned previously, the hills stopped that in a hurry.
At Leadville, I had met several people at the training camp that I knew would be shooting for a 28 or 29 hour finish. I spotted one of them at the start and tried to run at a similar pace. I was a little surprised that everyone ran almost all of the first 5 or 6 miles in the race. I ran behind her for a couple of miles then had to make a quick stop in the woods and rather than try to catch her again I just maintained the same pace, SLOW but running. (The first 5 miles is almost all downhill or flat.) After May Queen aid station, the run starts up a section of the Colorado Trail before hitting a well maintained gravel road that climbs gently for a couple of miles. The course then truns onto a steeper forest service road up to Sugar Loaf Pass. About half way up the climb I spotted her again so I figured I was going about right. (She was one of the people that was introduced at the training camp as having finished Leadville more than 10 times. That is why I choses to follow her.) A few minutes later I noticed she was not ahead of me anymore so I assumed she must have hopped over into the woods, too. I never say her again until I was almost back to the Hope Pass Climb from Winfield, inbound. It was less than 10 minutes until the Winfield cutoff and I knew she would not make it.
At Wasatch I did not worry about pacing. I just started off about 3/4 of the way back in the pack and ran my usual slow pace. A few people passed me in the first few miles but mostly I ran with the same people over the lower section and up the first climb until I was slowed by the atrial fibrillation. There is probably little benefit in trying to figure out what a 14 or 16 minute pace is on a fairly flat course if you your race will be on steep terrain, but at least it gives you a sense of how slow you will need to be moving. Remember, a 14 minute pace is a 23.33 hour 100 mile pace. Take a look at the finish results of the race you are running and see how many actually beat 24 hours. At Wasatch in 2010, over 200 started and 16 finished in under 24 hours.