Odd performance issues - fxp vs xl?

[J. Seth Henry]

Guys,
I recently had a little run-in with lightning during a recent thunderstorm - 
which destroyed my FreeBSD based router (along with a good chunk of my home 
automation system...) 

The machine had a VIA EPIA mainboard with a 933MHz processor. I had two 3Com 
3C905C-TX boards installed for the router, and used the local vr interface 
for monitoring (although it was mostly unused). The machine had a 40GB ATA 
hard disk, and 128MB of RAM. It performed quite well as a router up until the 
storm. The machine ran a custom compiled version of FreeBSD 4.8, and I used 
ipfilter/ipnat for routing.

Now, I have a new machine with a Tyan S2425 mainboard, and a 850MHz Pentium 
III processor. The Tyan board has two Intel 10/100 Pro (fxp) interfaces 
onboard. The system has an 18GB Ultrawide SCSI drive and Adaptec 29160UW 
controller - and 256MB of RAM. (it was a workstation before being pressed 
into service as a  router). This machine had just been upgraded to FreeBSD 
4.10-REL - and I recently recompiled again to add some IPFILTER options.

The trouble is, the new machine routes much slower than the original. Even 
text based (ssh) traffic appears slower. X apps are always a bit slow, and I 
could always see the refreshes, but it takes forever now. 

I replicated as much of the configuration from the original machine as I could 
(same ipf.rules, ipnat.rules, sysctl.conf, etc). The new machine runs an 
identical software set (dhcpd, sshd, etc). As far as I know, nothing is 
consuming an inordinate amount of CPU time.

In theory, the new machine is better all around. More RAM, faster CPU, etc - 
so I am a little confused as to what the problem could be? It seems as though 
the network adapters could be the issue, but this is a broadband link 3Mb/s 
peak from comcast - to a 10/100 adapter???

I did enable the downloadable firmware for the internal network interface 
(link0), but turning it on or off doesn't seem to make a difference.

Any ideas?

Thanks,
-Seth