Justin loves that lens... so much so, I rarely get to use it. He uses it for the portraiture aspect of our business. Be warned, though -- it's a HEAVY lens. Heavier than the 300mm f/4 L lens I primarily shoot with. We don't have a lot of L lenses, but the few we have paid for themselves a long, long time ago!
PS: Excellent pics. Sorry I didn't post earlier. I've also looked at a handful of the ones you posted a link to in another thread. Enjoying the high shutter speeds to stop action, I see. Only suggestion -- compose, then fire. That way, you could get things like people's goofy (or intense concentration) looks as they prepared to throw (looked like disc golf, but I couldn't tell?) Makes for more interesting, compelling photos. But not every photo needs to be a work of art, and I'm the first to admit that. Photography should always be fun... and digital is the essence of fun, allowing you to experiment and do all sorts of things people really didn't do much when it meant film and processing costs just to "see what this does."