Alot of people like to got out fast and see how long they can hang on. I agree with the letsrun brothers that "even-splitting a race is the only way to go to get a world record in a long distance event." Or, more generally, even splits result in any optimal effort (the fastest one can run on that particular day). So I wasn't going for a world-record Sunday, but I did want to give the race my best effort. My splits:
1st half: 6.6 miles, 245 ft. net elevation gain, 57:36, 8:45 min/mile pace
2nd half: 6.6 miles, 245 ft net elevation loss, 1:02:11, 9:25 min/mile pace
That is a big positive split and emphasizes just how different trail racing is from road racing. On roads, I can hit mile mile splits within a few seconds of my expected time and I always slightly negative split, except for the two time that I've cramped at about 8k of a 10K. The result is, invariably a good race. At the Craig Cup 5K, I also have slightly negative splits, largely because I know the course and can run it blind. Again, I've always had good races there.
But a trail race, especially on an unkown trail, is very difficult to get an even split. If you go out too slow in the first half, all the speed in the world in the 2nd half isn't going to get you the place you could have achieved with something closer to an even split. But if you go out too fast, you bonk and slow hard in the 2nd half. Given the highly variable effort in a trail race, from mud to steep ups to steep downs to flats on hard surface to tight single track, it takes either huge skill to achieve that perfect (even-split) pace or an intimate knowledge of the course. So that's a skill to work on, finding that race pace that balances the too slow (creating a big negative split, which ends up with a sub-optimal time) and the too fast (creating a big positive split, again with suboptimal results).