see
http://www.gnutellaforums.com/showthread.php?t=56476 which is more or less the same question, however
this also depends on your own connection speed that you get from your isp and so on and without knowing details of your set up, speed and how you have set up your Limewire and so on it is hard to answer. The user guide linked below has some good tips in it.
Personally I have a maximum download speed of 55KBps off a 440kbps connection (440 divided by 8 = 55) but generally my downloads are about half that speed on LW, much like yours in fact... just to give you an idea....