Oh that looks promising and it`s easier than my current solution. Thank you! For years I used the following small note saved on my mac to perform bandwidth tests of my application.

  #create firewall bandwidth configuration
  sudo ipfw pipe 1 config bw 15KByte/s

  #add config to firewall 
  sudo ipfw add 1 pipe 1 src-port 80

  #change. during testing
  sudo ipfw pipe 1 config bw 115KByte/s

  #delete. after testing
  sudo ipfw delete 1