most of my nigth games are shoot at iso 1600 640-800 2.8 with my 1dmkii's aswell.
this is shot with my 400 at 2.8.
i use Noise ninja in post prod. and levels/curves in Photoshop.
out towards the sidelines i have to drop as low as 320+ to get useable pictures.
try to use manual control and 2.8 and experiment with the shutterspeed and try not too get below 500 as the pictures will get motionblur.