3com 905c-TXM vs nForce2 LAN

[carage]

I've been using a 3com 905c-TXM for awhile and I am very satisfied with its performance.
However I would like to try out my nForce2 motherboard's built-in LAN, it's not the Gigabit LAN, just plain 10/100Mbps.
Which setup is better? Would using the motherboard LAN utilize more system resources?
How do I test the change in network performance accurately?

Thanks for any help.