I shoot a lot of rodeo events with Canon's 70-200mm f2.8 IS, along with a 1.4x teleconverter and love the results. I do not have the 300mm prime, but like other posters, prefer the zooming of my lens. In a number of events, I need to keep the rider or roper tight in the shot and would be unable to do so with a prime lens. I am constantly zooming in or out depending upon the direction of the bull, horse, wrestling or roping subject. It really depends on what you are shooting. For me, I would only use a long prime for beginning action at each gate. After that, the use would be more limited.