bittorrent speed way too low, what possible causes?

[stan]

Hi,

I used torrent to get the F7 live CD and DVD images.  And then let it
run overnight to seed.  I've tested my system with the online speed
sites and my upload is ~540 KB/sec.  My service from Cox says 512 -
2MB/sec.

Yet bittorrent-curses maxed out at around 70 KB/sec.  I used the
max_upload_rate = 0 to let it go at the maximum rate.  

I tried with the ports open and closed, no difference.

Is there something else that would limit the upload speed from
bittorrent?  

I don't mind running torrents overnight as seeds as nothing
else is happening anyway.  But at these speeds it hardly seems
worthwhile.