I would like very much to be able to analyze stuff like fq_codel under
bit torrent like loads.
I have some knowledge in this area which may help. You should be aware that BitTorrent may use uTP which is a TCP alternative that tries to eliminate bufferbloat. The main difference is that uTP targets a "full line" delay and adjusts its window size based not only on packet loss, but also on delay. Line delay is then forwarded back over the ACKs. uTP runs inside UDP.
You may want to analyze both things. I have a hunch fq_codel solves most of the trouble they had because it eliminates the otherwise standing queue. So be sure to test TCP-only client models as well as the uTP one.