well, i would suggest slowing your upload rate by about 5 - 10KBps (note that capital B represents Bytes and not bits) than it's maximum, thus allowing your BT client some bandwidth for communication.

I've heard slowing it down a little and allowing for some network interaction helps speed your downloads up. Something to do with the way the BT network works, i'm not too sure about the full details, but it certainly worked for me =P