I've heard some reports that the HPN-SSH patches to sshd are not quite working as well as expected, with some users getting mildly worse results. They're apparently supposed to improve performance:
https://www.psc.edu/hpn-ssh-home/ With "HPNDisabled" in sshd_config I notice no particular difference in sshd performance, but I don't have access to any particularly amazingly large machines currently.
