if that is the case you are maxing out your connection, most likely for very small periods of time. basically at some point in time more packets are queued up to be sent down your internet connection that the speed you have can handle, even if its only for a second or two. the difference obviously is that a program like bittorrent will constantly max your connection.
follow the guide on dd-wrt, set up your bandwidth limits in your router correctly, and, for example, set device priority by mac or ip address to your computer. then when the router gets too many packets at any point in time and has to queue them up, it will send yours first. not too difficult, but keep fighting me, by all means. i have no idea about anything.