Depends really on the specific conditions you are shooting under and what you intend to capture. For example, village green cricket on a fine sunny day will be fine but rugby/football under floodlights will probably challenge the 5D to the max. Depends a bit on your lenses though.
You then have the problem that the 5D AF points are clustered in the centre of the viewfindr so this MAY not give you the composition that you want with AF.
Next there is the number of fps which is a bit low on the 5D for action sports.
Then there is the responsiveness of the AI servo mode which you might use. This again is not the best.
Oh yes, then there is the weather sealing...
Lots of people will advise you that you CAN get great sports images with the 5D but you might find it a bit frustrating for low light action shots.
I do have a 5D1 but would always pick up the 1D3 for sport to obviate the above, and other reasons.
Personally, I would look at a used 1D2N for about the same price as a decent 5D plus grip, or, if you want to push the boat out a bit try a used 1D3.
Basically, a 5D CAN get good sports images it is just so much easier and effective to do so with one of the aforementioned bodies.
Good luck in your selection.
