I have successfully used Wonder Shaper for some time to help my “temperamental” Comcast cable modem connection. I am able to upload/download while surfing and using a VoIP line.
I recently did a clean install of the custom 6.01. My 3000+/256 Comcast line tests averaged around 2100/150 over a 10 day period. I added the QOS panel and tried several settings over 2 weeks and achieved a small improvement. I re installed Wonder Shaper and again saw a dramatic improvement. My connection is averaging 3050+/225-248.
Take a look. Below is a link to the rpm I used.
http://lartc.org/wondershaper/