You didn't say anything about #processors or speed, norGood point, and may I note that you *can* choose your encryption, I use 'blowfish' for normal operation, since I have some faitly slow machines with a Gbit net between them.
did you say anything about your hard disk's raw-io ability.
You also didn't mention what kernel version or whether or not
you were using the new UID-group cpu scheduler in 2.6.24 (which likes
to default to 'on'; not a great choice for single-user, desktop-type
machines, if I understand its grouping policy).
Are you sure neither end of the copy is cpu-bound on ssh/scp
encrypt/decrypt calculations? It might not just be inability
to read from disk, but low cpu availability. Scp can be alot
more CPU intensive than you would expect... Just something to
consider...