I like a forum board to be in between (more towards the 'wider' look), where as you have the forum, but yet you have a nice background trim that gives it some decoration (or a solid color - whatever it is).
it depends on the quantity readable content that's usually posted on your boards ... I see some of the threads in your forum have a lot of content to read. In this case you should ideally keep the board wide but not too wide. it's easier for humans to read top to bottom than left to right but having too long a thread can make the reader un-interested.