Yeah, I think IE does 4 simultaneous by default. Of course, you can tune that number up in the registry if you know what you're doing. Not sure what Mozilla/Firefox does. But frankly, its only a matter of simultaneous connections. I think I would be able to eat the same amount of bandwidth either way.
Perhaps throttling is really the way to go. You might be able to establish some sort of QoS using your router, where your personal stuff takes a higher priority than the forums.
Just a thought. Either way, we appreciate you running this place for us!
-Andy