On certain connections, for example through some wireless devices, FreeBSD ssh/scp will copy data very slowly. Typically I see copy rates at 1/3 normal speed. This is happening because the IPQoS option for both ssh/scp (ssh_config) and sshd (sshd_config) default the IPQoS setting to 'af21'. Changing this setting to instead default to 'lowdelay' will produce normal data transmission speeds out-of-the-box for new FreeBSD installs thus making many users happier not having to trouble shoot and track down this weird random problem when it occurs. The low speed transmission issue only occurs on some connection paths, mostly I have seen it happen when copying data through a wireless bridge or access point. In hind sight, I see that on Linux, Openssh DOES default IPQoS = lowdelay, and perhaps that is not by accident?
The IPQoS setting for the non-interactive sessions also needs to be changed from 'cs1' to 'throughput'.