I tried to transfer a CD image (around 600Mb ) from a local network linux
machine to a windows machine with the cygwin sftp. The transfer is very
slow. It did not go beyond 15KB/s But I did transfer it just with ssh and it
was pretty quick.

ssh logu@ "cat sysrec.iso" > sysrec.iso

What could be the problem. I have switched off Antivirus, firewall etc. Also
I tried with ssh.com sftp2 client and it was also very fast.

The version of the cygwin openssh sftp client is: OpenSSH_3.9p1, OpenSSL
0.9.7d 17 Mar 2004

Any help will be appreciated.