[Samba] Network transfer speed issues in RHEL4

[Phusion]

I am in need of some help with a speed issue on a test Red Hat server.
The server is running RHEL4 ES Update 4. When copying a file using FTP
it transfers at 19GB per hour, but when copying via SMB it transfers
at 3-4GB per hour. The network card on the server is Intel 10/100.
When copying using samba a simple cp -av command is used. I have
tested when this server is part of Active Directory and when not with
the same results. Also, I've tested enabling and disabling selinux
with the same results.

Operating system: Red Hat Enterprise Linux ES release 4 (Nahant Update 4)
Linux kernel: Linux 2.6.9-5.EL i686

Samba packages installed
- samba-common-3.0.10-1.4E
- samba-3.0.10-1.4E
- system-config-samba-1.2.21-1
- samba-client-3.0.10-1.4E

Samba configuration file
[global]
workgroup = ABC
realm = ABC.LOCAL
preferred master = no
server string = Samba file server
security = ADS
encrypt passwords = yes
log level = 3
log file = /var/log/samba/%m.log
max log size = 50
winbind separator = +
winbind use default domain = No
printcap name = cups
printing = cups
idmap uid = 10000-20000
idmap gid = 10000-20000
winbind enum users = yes
winbind enum groups = yes
template homedir = /home/%U
template shell = /bin/bash
password server = dc.abc.local

Samba mount command in startup script.
mount -t cifs -o credentials=/etc/.samba_cred_backup_server,rw
//webbackup.abc.local/backups /mnt/backups
# cat /etc/.samba_cred_backup_server
username=nasuser
password=nasuser

I would appreciate any ideas on this. Thanks.

Phusion