Caffeine as a performance enhancing drug

As an amateur endurance athlete, I often for ways to improve my Speed and stamina.
It seems to me that nutrition, training and technique is the key. Of course looking for the right ones are the challenges.
I do not consider doping as an option, considering the side effects that it may have on the body in the long term, as most drugs have negative side effects. In addition, I prefer not to put anything synthetic into my body.
Caffeine is interesting though, it is part of most people’s daily diet. I wont drink redbull or livita, I have seen some athletes drink this before an event. But i do drink the occasional tea.
Found article online that briefly describes how caffeine pills are allowable in certain doses, and the effective use of it. Generally the people who would benefit most are those who rarely take them. So dont take them during training, but take them for an event or competition.
I personally have tried drinking caffeine in the forms of tea and coke before a run. In my 70.3 ironman it was my first time I saw coke prepared at the water stations. I admit there is a boosting effect, I do push myself harder to the point I am faster for longer,  but i noticed that it felt more hotter, and I was more thirsty,  I felt more hotter as well. And my body does hurt more the day after the run.
If anyone wants to try to get a personal best, or to train faster, then go ahead. I personally might not do it. Plus I am not that competitive. But if you are, caffeine is the one legal way you can do it.
http://www.runnersworld.com/rt-web-exclusive/how-to-boost-long-distance-performance-with-caffeine