Hey,
Agree with roseway those stats are perfectly fine. Try running a speedtest on that website roseway give to you when you are experiencing the throughput issues and also run another one when your not experiencing throughput issues to match the results. Also try breaking it down aswell by disconnecting anything that is not adsl related 1 at a time running the speedtest. Examples of non adsl equipment is the likes of phones,sky tv,splitters,fax machines, alarms etc. Also run the speedtester on 2 different machines aswell i would suggest.
Regards
Gary