Laurens, I think that there may be something else going on.
As an example, I've been updating
http://www.elsua.net/feed/ for about 90 minutes, and it's stuck at updating 54%. The CPU is running 99%, and the Windows Task Manager says that the process is running 1,226,696K. At this point, I'm shutting it down.
Yes, the three feeds I suggested tend to have a lot of links, but all of the others complete within 5 minutes, whereas these ones can run for hours.