I am currently torn between two different lenses for my Canon XTi and I am asking for your help to decide. A little bit of background first. I use my cameras to shoot my son and daughters sporting events. I just started the third season of my sons football and I am using my Xti and a Canon EF75-300mm f4/5.6 non-IS. My shots are better then last years when I used my Canon S3 IS w/1.4 extender, but I am not getting the sharp crisp images I thought I would get when I upgraded to the XTi. I have been researching the Canon EF75-300mm f4/5.6 IS an the Canon EF100-400mm f4-5.6L IS. The 400mm is almost twice as much in price but the reviews have it written up to be a very sharp lens. Does the Image Stabilizer in the 300mm really help with getting sharper images? Is the extra money for the 400mm worth it? Has anyone had experince with both of these lenses an would be willing to help me decide?