it could be your firewall, network settings turning down the connection speed, could be a hop along the path not working right (run tracert and see), dns, it could be because you are downloading a crap ton of small files, they just take a long time. Your ISP can also throttle some connections. 6Mbps is really not that much (less then a megabyte per second), so with variable drops that normally occur you are getting somewhat expected speeds. Are you within the area where a lot of wifi networks? You could get noise interference. Try connecting with a cable if that's the case