some thoughts
1) setup a second network on dedicated network cards force it to use the correct nick by using the iP addres. possible reduce the network traffic
2) could use a cross over cable direct connection and take the network out completely.
3) use a bandwidth limiter so as to not saturate the network, set it to something like 75mb upload on server, so your gaming has 25mb to play with.
might get some better advice from the networking and connectivity sub forum