Is the NIC connected over USB?

[tllim]

does this gbit nic actually provide gbit speeds or is it limited due to how its wired onto the board?

Most Allwinner SoCs have a native GBit Ethernet implementation called GMAC/EMAC (on the A64 multiplexed with the LCD interface!). This will be combined with an external Ethernet PHY through RGMII -- so no USB involved. The RTL8211 used on the Pine64 acts only as a PHY so you'll need neither RealTek drivers nor do you get RealTek features (Wake-on-LAN for example). It's just responsible for the physical layer.

The theoretical throughput depends on many factors. Given the theoretical single core speed it might be possible to reach the theoretical 940 MBit/s.   But CPU speed isn't that important -- it's more about balanced network and I/O bandwidth: And there the older A20 clearly outperforms the A64. If it's really just about file serving, a pcDuino3 Nano Lite is the better (and cheaper) choice. Some background informations:

http://linux-sunxi.org/Sunxi_devices_as_NAS

@tkaiser, thanks.

 Not trying to be a dick here but where do you get GB speeds? Local networking?
On a side note, I worked as a contractor for an R&D firm a while back, I distinctly recall the head boss dude mentioning that the people at realtek were serious assholes

I have gigabit Internet connection at home, but yes this is mostly important on local network, for example to access shared storage on a pine64 cluster.

longsleep has tested the current GB speed on Pine64 about 500Mb plus, there is still some room to improve further.