I mostly agree with sando...
sando wrote in post #5277686
With an XTI? I'd go for the 17-55 2.8 IS instead. You'll find 24-70 not wide enough at the wide end on a crop body.
Then I'd save up for the 70-200 2.8 IS
I have both the 17-55mm f/2.8 IS and 24-70 f/2.8L lenses and I find the 17-55mm lens a more versatile glass on a 1.6x camera. It is especially better on a Rebel (series) camera because of its lighter weight. IMO, the 24-70L doesn't balance well with that heavy lens. A battery grip helps but, the lighter 17-55mm lens is the ticket for the small Rebel (series) cameras.
I mesh my 17-55mm f/2.8L with a 70-200mm f/4L IS lens. These two are a super combination. The f/4L IS is a lot lighter than the f/2.8L and matches with a Rebel (series) camera better because of its weight.
I carry my 17-55mm and 70-200mm f/4L IS lenses everywhere on 2 bodies. I think that I would seriously balk at carrying the weight of the f/2.8L IS lens on some of my more rugged photo excursions; especially combined with the weight of the 24-70L lens.
I don't usually require a wider lens. I can make do very well for most shooting opportunities with the 17mm as my widest focal length and I don't miss the range between 55 and 70mm one bit.
The f/2.8L might be a smidgen better for isolating individual athletes but, for general overall shooting - there is not much you cannot do with the lighter weight f/4L. Get the f/4L IS lens AND an extra body. You could get a used extra body for the difference in price between a f/4L IS and an f/2.8L IS 70-200mm lens..
Those two lenses on two bodies really make one heck of a wonderful setup.