Hi,
I'm sure some of you stumbled upon this one, but for those who haven't I recommend this read.
It is a very good read on where different sorts of queues reside in Linux.
http://www.coverfire.com/articles/queueing-in-the-linux-network-stack/
The author covers a lot of ground including TCP Small Queues, Byte Queue Limits, etc.
Also provides his own qos script and some interesting things like the fact that txqueuelen is only used as a default queue length for *some* of the queueing disciplines, not all as others have it governed by tc.
Best regards,
Maciej Soltysiak