You should never have your upload in Azureus set to 100% of your NTL upload speed. If you do this, the torrent uploads start to get in the way of the data your PC sends back to the internet to acknowledge receipt ofstuff you are downloading ('ack packets'). If the ack packets don't get back to the source of your download, the next piece of the download is delayed, hence you see your overall download speed drop.
Others will be able to advise you on the exact settings that will work best for you.
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to the forum by the way.