In the interest of setting an upper bound on routing performance for 
m0n0wall, I'll give one example..

Opteron 1.6 Gigahertz
Dual Channel DDR400 Registered ECC 1024MB
2*64-bit PCI-X Broadcom Gig-E Adapters

Performance:

Port to Port: 55.47 MByte/S, 554.7 MBit/s (Maximum Gig-E throughput 
without jumbo packets and frames).

When I messed around with the BSD kernel settings and went to jumbo 
frames, I got ~70-80 MByte/S on separate trials piping 10GB test files 
port to port via FTP. I also increased the TCP buffers in m0n0wall and 
the linux server/client.

VSFTPD serving the data on one side and ncftp receiving on the other. 
The client and server were dual opteron 2.2's with 2GB of ram, running 
Fedora Core 3, with matching ethernet adapters and matching frame size 
settings. They had identical Broadcom Gig-E adapters. They were plugged 
into a D-Link XStack DXS-3350SR with jumbo frames enabled.

Basically, once you reach the opteron range (which can be had in 
extremely low power varieties), you get full Gig-E routing performance.

We're building a 1U opteron 246 (2.4GHZ) with 512MB of dual channel ECC 
that we'll be using as a firewall/router for our grid computing farm 
we're building. We're puting in a Soekris VPN1401 PCI card for VPN 
connections to manage the farm. We purchased a compact flash to ide 
adapter and will be running a Sandisk Ultra II 256MB adapter (that's 
what I run in my Wrap 1C-3).

I'd be happy to give more specifics on hardware if anyone is interested.

Michael Joy
HEP - University of Mississippi
mdjoy at phy dot olemiss dot edu