[MovedGoalPosts]

As far as I'm aware the WRK is a lightweight router, compared to the WRT series. That could be a part of the problem. I've never used static IPs on my networks always allowing the router to do the work with everything set to autodetect. If the torrent is throwing out loads of connections it could stifle other traffic.

If you want to prove the broadband is OK, then try with just one PC connected direct to the modem, no router. Then you will know where to look.