I have had the most luck with this type of issue by turning off Nagle's Algorithm, Bandwidth Delay, and Slow Start (which along with the buffer sizes are the primary settings changed in the default tcp-lan-optimized profile).
Nagle's especially seems to be the culprit, because it tries to buffer small packets instead of immediately sending them on the wire, and delays ACK responses as well. Ostensibly, it is designed so as not to flood higher-latency networks with a bunch of small packets, but in practice it seems that it introduces a lot of latency even on long RTT networks.
Denny
Cirrostratus
