I tried the RTL8111C which was half the speed under FreeBSD in Windows.
Using Windows’ built-in driver (Windows 8) resulted in similar performance (900 Mbps send, 600 Mbps receive) but installing the driver from Realtek website resulted in way better performance at 900 Mbps both ways.
I got similar result under Windows 10 for a different system with onboard Realtek chip. The lesson is make sure to install manufacturer’s driver it seems.
Also interesting the driver name says TP-Link gigabit card instead of Realtek. The card is indeed a TP-Link card but I don’t often see brand-specific name come up from a generic chip driver.
Now I wonder how it performs under other operating systems. Maybe I’ll try it sometime later.