Pretty specific question.

[Insanity]

I'm currently looking to buy a lens for a Canon Rebel XS and for use on a T1i later on.

The first mission for this lens is going to be night time open air stadium shooting. My main question is would a Canon EF 70-200mm f/4.0 L USM Lens be good enough for this purpose.

Canon EF 70-200mm f/4.0 L USM Lens Review

Also, how far away can you be from a person and still see facial expressions? I'm looking at being in the bottom section of the stadium at the moment.

Edit: This is gonna be a monster truck show, so the lens will be on Auto-Focus most of the time as well.