Firewall & DSL performance

[Darryl Hoar]

Greetings,
I have a dedicated older box that is running Freebsd 4.7-stable,
IPFilter and nat for my home network.  It has a 3com 10Mb 
ethernet adapter plugged into the dsl jack (we don't have /need
dsl modems as we have fiber to the house).  The other NIC in the
firewall is another 3com 10Mb which is plugged into my Linksys 
10/100 switch.

Problem:
Recently, our ISP upgraded (at no charge) our connection from 512K to
1.5Mb.  When testing from a computer on my Lan, I was only seeing about
700K.  Testing at the box on the side of my house yielded 1.5Mb.  Testing
at the jack inside also yielded 1.5Mb.  So, my firewall seems to be
slowing things down.

I am using CAT5 cabling, and quality jacks and patch cables (hubble).

Any ideas where to start on determining what is causing this slow down ?

A friend that also has the service is running Windows 2000 Pro, Norton 
firewall and zone alarm and has no problem getting 1200K.

thanks for ideas,
Darryl