I did one last year and I think I took 8th place out of quite a few riders. It was a rolling short course out and back into a head wind. I am quite sure I would have done better on my road bike with gears for this TT but my road bike's seat collar broke so I was forced to ride my fixed wheel bike. I think I ran a 46x15 which was actually quite a good gear for the rolling terraine and was using bullhorn bars. The 180 degree turn around can be a little tricky too.
I always bring my fixed gear bike to TT's but if there is a bad wind or hills in the course I will opt for the geared bike.