I don't think the Canon 17-55 focuses much faster. Have you considered using a focus assist lamp? (Such as what comes with the 430EX or ST-E2.)


The 70-200 f/2.8 non-IS is an excellent choice for sports, especially because the shutter speeds often make IS unneeded. The image quality on that zoom is almost as good as the prime you shoot now.


However, on APS-C, while I find that 70-200mm is an excellent range for sports, to me it is not long enough for wildlife. The 400mm f/5.6 is better for that purpose, but it's not a zoom, and the 100-400 is $300 over the price range.