Personally, I'd say the 100 f2 would do the job a treat. I like prime lenses (ones which don't zoom) as I find that it's one less thing to think about, which results in me improving my composition with what I've got. Another benefit is that the "jack of all trades - master of none" theory, where something which is specifically designed to do one job, will do it better. You will generally get a lower f-number and therefore more light with a prime lens. However, you're stuck with it's length... It's a trade-off.
If you value highly sharpness, low-grain and the ability to take a shot fast, I'd say a prime is the way to go. However, if you want flexibility then get a sensible zoom like the 28-70 or 70-200. I personally have a 20mm and a 105mm which go everywhere with me. The lenses I don't always take are a 180mm for long situations and a 50mm (1.2) for low light. If I were going to your event, I'd stick with my 105mm as it's a 1.8 and it's going to be fine in that kind of light with a 400 ISO film which isn't going to break down and go grainy (like a 3200 would).
Horses for courses and all that.
Hope I've helped rather than confused!!!
Rob