i have no problems with downloading.
but i mostly download old stuff / tv-series / ... from specialized trackers...
if you think you are banned try:
-P xxxx
this will fake the peer-id i suppose
a list of peer-ids you can find here:
http://wiki.theory.org/BitTorrentSpecification#peer_id
i haven't tested it yet, but i think it works...
concerning -C 0 cache option:
i only have 32MB of RAM on my wl500gx. i don't want to fill up the whole RAM with cache. i have mostly up to 10 torrent in seeding mode and 3 in leeching mode.
http://wl500g.info/showthread.php?t=6161
i've also read from some Fritz-Box-Users who are disabling the cache because of performance reasons.
but i didn't really checked it.
i'm satisfied with my results, so i had no reason to change the parameters.
the only sad thing: i have to reboot the asus from time to time (about 1-2 times a week), because it is hanging.
maybe you should reboot your router to gain the same performance like 1st DL.
greetings