Hi All, for years I have drooled over the Canon 70-200 L lenses - not that I have any experience with them, but probably because lots of folks rave about them, and because they are way more than this wannabe needs to - or should - spend on a lens. Been considering a used non-IS version on local craigs list. I don't think I would miss the IS. I want this lens primarily for sports shots. But my sports shots are mostly outside baseball. So my question is, do I really need a 2.8 for what is primarily daytime, full sun (or overcast) shooting? I use my Canon 40D kit lens and also my Sigma 70-300 (I assume f/4) mostly. (Fwiw, I've never felt my 40D gets as crisp shots as my Rebel XT does. I plan on doing a side by side comparison next tournament weekend!) Wondering if the Canon lens would produce significantly clearer shots? Is the aperture the main factor for driving the cost? Or are there other qualities (glass?) that factor into this? Also, has anyone here used an extension with this? Does that reduce the benefit of the 2.8 enough to just say "stick with your Sigma"? Thank's y'all!