FIXED BY DISABLING QOS IN NETWORK ADAPTER PROPERTIES - DUH.
I recently build a home server with this motherboard and ASUS doesn't seem to support the Server 2012 R2 operating system.
So I went to the Intel site and downloaded the LAN controller manually aswell as the other drivers (Intel HD / MEI etc).
However, I'm getting 40Mbps download (w/ speedtest) even though my ISP's speedtest on another PC (connected to same switch/router) indicates that I have 95Mbps.
Switch - OK
Cables - OK
Nothing is being throttled and QoS is disabled.
Is it because I'm not using the official ASUS driver for the Ethernet controller?