Does it get choppy? 40Mbps is plenty for online gaming.
Is there actually a problem?
What really matters is your cable/dsl modem - what kind of internet package do you have? If you have a 20Mb internet connection, it doesn't matter if your N drops to 40Mbps - it's still plenty of bandwidth to game out.
Crowded WIFI can cause lowered speeds, incorrect WIFI card settings, router settings, basically there's tons of things that can go wrong with wireless, especially if you don't know what to look for.