sftp/scp performance testing

[Mike Perham]

Folks, I've noticed poor performance using sftp.  If anyone has any
advice on how to improve performance, I'd like to hear it.  Test simply
involved transferring a single 143MB MP3 file using defaults for all the
program configs.  The opensshd 3.0.2p1 server is used in all tests.

Software:
openssh suite 3.0.2p1
psftp (putty sftp client) latest dev snapshot
pscp (putty scp client) latest dev snapshot
winscp 2.0 beta
cygwin 1.3.6
windows xp

Localhost (client/server on same box)
opensftp - 5.5MB/min
putty sftp - 6MB/min
open scp - 56MB/min
winscp2 - 95MB/min
putty scp - 280MB/min
windows copy - 780MB/min (11 sec)

10mbit LAN (same binaries, both xp machines)
putty sftp - 1.2MB/min
opensftp - 3.9MB/min
winscp2 - 9MB/min
open scp - 50MB/min
putty scp - 65MB/min
windows network copy - 68MB/min

I should also add that these machines are both P3 or better and both have
half gig of ram.  None of the secure tests peaked the CPU or gave any
indictation of a net/IO bottleneck in the task manager.  I imagine the two
windows copy tests were peaking the IO/net bandwidth.

Questions:
why is sftp performance so much lower than scp performance across the
board for this simple test?  Does this point to a server-side issue?

Thoughts?

mike