speed problem..

[nox]

hi..

i'm using deluge on debian testing.. my connection : 6mbit dsl

but my download speed never reachs full capasity.. generally it dowloads between 250-350.. never saw 400+ , on my other computer which is windows based, with another torrent client when i want to get the same torrents it works 500-600..

so anything i dont know about it ? what this problem caused by ..