Network card selection / recommendations ?

[Andrew Seguin]

Sorry for distracting with such a question as to recommendations as to 
network cards, but since I'm planning on upgrading a freebsd firewall 
(currently running 5.4-STABLE), I'll check with those who know the best!

At the moment I have a firewall/router based on three fxp intel nics (a 
cheap sis card serves for management purposes). I'd like to upgrade to 
gigabit network cards (because our internet connection will be getting 
an upgrade from an SDSL link to a 100mbit connection in the near 
future). I've liked Intel to date for their 100mbit cards... but a few 
questions come to my mind before I chose a gigabit card, questions which 
I hope the community here can answer for me or help guide me into a 
solution.

First off, several gigabit network cards advertise various kinds of 
network cable diagnostics (Intel "Advanced Cable Diagnostics", D-Link 
"Cable Diagnostic",for example). We have in one building here old wiring 
that wasn't professionaly installed and in most places only 10mbps works 
although the wires are certified cat5. We don't have the money for a 
good network tester with TDR to find out what kind of problem exists 
(although a simple pin-out tester says there are no crossed wires). So 
question number is really this: does anybody have any experience with 
this kind of functionality on a network card? is it worth anything?

Second... is there any advantage to dual port cards in term of 
performance? I always imagined there could be a solution which could be 
a big performance boost if a packet came in one port, the headers only 
went over the PCI bus for processing by the OS, and then the 
firewall/gateway for example either tells the NIC to delete the packet 
or forward it off the second port (all without copying the entire packet 
into system memory). Is that just my imagination of a perfect world or...?

Thank you all for sharing your wisdom!
Andrew