Hi zombie.......
5 to 8kbps on a 56k dialup is doing pretty darn good!. Most dialup users only average around 4 to 5kbps, or less.
You didn't say what OS your using. If you are using 98/SE there are some "manual" dialup networking and registry tweaks to help. Its been awhile since I've used 98/SE, but I'll look for them.
Once you go to cable....check out... SpeedGuide.net....lotsa GREAT tweaks to get the most out of your cable modem connection.
Hope this helps.