Hi, My primary lens for my Canon XTi is the Tamron 17-50mm F/2.8. I am looking for more reach in order to photograph my kids in martial arts and dance. Given that these are both low light situations, the F/2.8 has been very helpful. But 50mm isn't getting me close enough. Last year I rented the mac daddy Canon 70-200mm f/2.8L for my daughter's dance recital. Wow. Simply amazing. But at $1600+ it's not going to make it into my camera bag on a permanent basis any time soon. So my question is, should I be looking at something with more reach but less f-stop such as the Canon EF 28-135mm f/3.5-5.6 IS USM? Or should I consider a fast prime such as a 100mm or 135mm f/2.0? My concern with the prime is that I will not be able to get any wide shots such as group shots. Also, in martial arts the action moves around the ring pretty quickly, usually changing the distance between me and the players. Dance tends to move side to side so the range is usually more consistent. Thanks!