Some folks' internet connection won't handle their framerates because they are too high, and some folks connections are good enough to flood servers with attempts at 120 fps updates, and, oddly enough, not every 'server' (often just a PC hosting a game, in reality) has the bandwidth to service 32 players with 60-120 fps framerates. See if the computer feels sluggish with the single player game portion before assigning blame on cpu and/or gpu. You might just need to connect to a better server with a better connection.