Another idea i had was for the active torrents. Since it's very hard to know the speeds and/or number of seeds you have on torrents it can be a bit tricky to set the allowed number of active torrents to a good value.

An idea for this could be "If global download-speed exceeds X kb dont start new torrents" and "if global download-speed is below X kb allow 1 queued torrents to start" and prio of torrents could either be manually set or just in the order they where added so the oldest gets started first.

A variable limit, I don't know. Speeds vary all the time and it might temporarely dip under the limit, which could result in a torrent being started.
And then when it dips again, you could start another torrent ...

hm, maybe something that looks on the avg bitrate for the last 10-20 minutes or something like that.. My primary concern here is that i get torrents from a few different places and from some i usually download at around 90-95Mbit while other places are around 1-2Mbit, and ktorrent really hangs at those high speeds if you have 2 torrents running each at around 4-5Mbyte/s.

Maybe a better idea could be "Dont start new torrents if speed is above" and then maybe have some type of timer that will only start one torrent per 5-10 seconds to allow it to initialize before checking if the next one should run?

Just some ideas..