To be honest, your visitor sessions are not as high as I expected. But, you are chewing through a ton of bandwidth. Not so much now, but in the season you were consistantly shattering (almost doubling) your bandwidth allotment. In July you topped out at just under 35 GB.
Now though, according to your stats, you should be fine. If I were you, I'd try scaling back the number of topics displayed on the front Reds front page. Also, consider dropping the number of posts displayed on a page in a thread.
Then, watch your daily stats page specifically the KBytes column:
If you notice a significant drop, that might get you through the offseason. When the season starts up, you should definitely lean towards getting 35GB of transfer. Especially if they are going to start charging you for overages. I guarantee you the difference between 20 and 35 will be a lot more than $15 a month.
But, it looks like according to your stats, you haven't busted your monthly 20GB limit since August. If you are still having problems, it makes me wonder if your host just cant handle the bandwidth they are giving you. Switching hosting companies could always be an option.