Yes, the Mac & PC will see each other on both NICs.
Your intention is to connect the two machines directly with a gigabit connection for file sharing only, right?
If so, I would allocate static IP addresses to the two gigabit NICs on a different subnet to that being used by the router
For example, if the router is handing out addresses in the 192.168.0.x range, set the Mac's gigabit cable to 172.16.0.1 and the PC to 172.16.0.2
Then, in the Finder on the Mac, use Go > Connect To Server... and connect to smb://172.16.0.2 to make sure you're connecting with the right NIC. On the PC use \\172.16.0.1 in the Start > Run... menu to connect to the right NIC on the Mac
You may need to rearrange the network priority on the Mac in System Preferences to get to the internet as the Mac might prefer the faster connection by default
Hope this helps
-mrwalker