With snowboaring/skiboarding season underway I am very interested in getting many action shots on the slopes and terrain parks. I haven't been out to the slopes yet with my camera and the only lens I have now that I would be able to use is the Sigma 28-105mm f/3.8-5.6 UC-III Aspherical IF that came with my Canon 30d. The f/3.8 seems pretty decent for the relatively bright white snowscapes but I don't have any other experiences with lenses to compare image quality and AF speed. This lens is very cheap so I'm guessing that neither are top notch. I have about $500 to get a new or used lens. Yes.. I would love the EF f/2.8 70-200 USM lens or even the f/4.0 but that cost is just out of the question. Help me out here please. I will also use this lens for other sports such as soccer, paintball, baseball, and any other fast moving shots..