I've always used a "no caffeine" flavor. What is the benefit of a caffeinated one at a race? When to consume it/them, if at all?
I personally cannot stomach anything besides sports drink during under 2hr mtb race.
I do take 200mg caffeine tablet (stay awake generic brand- like "no doze" ) 30 min before race or hard ride - of course, test in training before using in race
Joe Friel's Blog: Coffee and Competition
Caffeine is a vasodilator, so you get increased blood flow and increased heart rate. I've found if I'm in a hole and only have maybe 20-30 minutes left of racing (and have an empty stomach) it's enough to get me through.
BUT caffeine is also a smooth muscle relaxant and will "mobilize" your last meal. People react differently to it though so, try it in a workout and see how it works out for you.