The only way to know if it's going to work for you is to try it during a long run before the race. A minimum 6 mile run should give you an idea of how it affects your stomach. A 10 mile run should give you an idea of long term affects.
Before going primal, I've used Fig Newtons. But I still plan on using them. It's neat (not sticky), easy on my stomach, and gives the same calorie content as GU. Plus it's cheaper. I'm just looking for it to give me a clarity-shot.
Running for mediocrity since 2003