If you have another host on the network using the same internet connection, the 2 basicllay SHARE the bandwidth. If the wireless client is doing alot of downloading, the the wired client will get bad performance in online games. The bottleneck is the internet connection.
Try turning off ALL hosts on the network except this PC, and trying to play the game again. If there is still trouble, it could be a trunk with some latency between you and the game server.