First off, I love Ktorrent and want to thank all the people who have worked so hard in the past months making this great client.

However, Ktorrent seems to lag behind uTorrent in its ability to get and keep download speeds high, when behind a firewall. Note, in my experience when KTorrent is on an open connection it will generally max it out, which is great! Now, implementing PEX helped a great deal, but something else seems to be involved. I'd like to get some ideas from people who know more about the BitTorrent protocol than I do, but here are my two guesses as to why uTorrent is faster:

1) uTorrent implements some kind of Qos to help find peers with less lag or closer connections and thus faster speeds. I'm fairly confident KTorrent does not do this yet.

2) uTorrent implements some kind of lax timeout. This prevents peers from disconnecting due to lag from a firewall. I only mention this possibility since a manual announce generally will speed up a KTorrent download (without introducing new peers) where the same on uTorrent has little effect.

3) Maybe there are some underlying network issues? I haven't tried uTorrent under wine (but heard it works), so its possible some fundamental difference in Windows and the Linux/ *nix network stack is the cause.

EDIT: uTorrent under Wine can keep 1/2-2/3 of full speed when firewalled, which parallels results under Windows so 3 is out. Also, with the exception of some minor tray issues, uTorrent (1.7.5) works flawlessly under Wine (9.44).

No issues here maxing out a Gbit connection with ktorrent behind a firewall here.

I can't duplicate any of your issues. As a matter of fact, I have the opposite.

I recently upgraded my home line, from 512 kbps up to 1 Mbit upload, and an increase from 7 to 10 Mbps down.

On popular or just plain well-seeded (i.e. lots of Swedes and Japanese peers) torrents from both private and open trackers I max my incoming speeds. I ran comparisons with Speedtest.net and with files from my Usenet, which always peg my download speed.

I am firewalled with ports forwarded, and over an internal wireless network. Nothing wrong with my performance, and it matches anything I've seen on uTorrent, Azureus and Deluge.

I also see solid, steady peer connections, no connect/disconnect implied by dropouts due to timeouts.

I'd be more concerned with your set up. My personal experience is that KTorrent has no incoming issues. That, or peers may be showing a preference for other-than-KTorrent.