Recently I thought I'd try a different program, and discovered that most of them wanted access to the controls of the hardware firewall in my router, and the documentation said that they'd be much slower without it.
So I looked at various suggestions and eventually installed μTorrent which has some very good reviews and is by far the smallest of the bittorrent programs, and enabled UPnP compatibility of the router and its firewall. This does seem to speed up file transfer immensely - I'm typically seeing 50k downloads now, a threefold to tenfold speed increase.
What I'm wondering about is the downside (apart from all other internet access being slow because file transfers hog the bandwidth and are prioritized at the router); does this increase the vulnerability of my network? They say not, but I'd appreciate feedback from anyone who knows this stuff. Presumably the UPnP thing means that any malware that gets onto a network computer may be able to bypass the hardware firewall, don't know if there are other risks.
Later: I posted this a couple of places, someone suggested this site which helped me configure it manually: