The NIC's are bigger because they're actual cards, not a chip on the motherboard.
I plan to use the HP as a Linux web browsing machine and my custom build as a gaming machine.
So both computers need to be able to access the internet (without sharing, so one computer can access the internet without the other being on).
And overnight copying isn't an option as the computers are in my bedroom, they're too hot and noisy to sleep with.