Ehh, the F2.8 just means it's better in lower lighting and you don't need IS for action/sport shots. Just need to upgrade the person behind the lens yeah?
Sorry, that came across wrong... Lol, I would recommend the F/2.8 for sports. It's fantastic for low lighting which is most of the time due to terrain, and in good lighting you have shutter speeds upwards of 1:2000.