I have asked our main Server Admin this question.
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But we have ran 5 COD4, 3 COD5, 2 TF2, 3 CSS on our box at one time, normally only 60 % on these had more than 10 players on at anyone time. we had no issues. Our connection was only 10mb uplink max peek. As for bandwidth usage I will have the asnwer hopefully later today.