[sketerpot]

I wonder how much of this is just because you're using a slow encryption function. On my (quite fast) machine, the default 128-bit AES encryption can handle a little under 800 Mbit/s. Meanwhile, Threefish-512 can encrypt at 4 Gbit/s on the same machine, with what we lightheartedly hope is an equal or greater amount of security. And if you use CTR mode for block chaining, you can parallelize it among however many cores you have, for several times speedup -- my quad-core machine could manage 16 Gbit/s with Threefish-512 in CTR mode, which is really quite zippy.

What I'm saying is, faster transfers should be possible. And they probably already are, if you're willing to find out how to tweak the OpenSSH settings. Maybe.