Just to add to this, we've got the same problem with our Arma 2 server. Max SFPS is 46-48 empty.
Specs as follows:
Leased a new dedicated server from Hetzner
Windows Server 2012 R2
i7 4770, 32Gig, SATA3, 500Mbit+ down 500Mbit+ up. (You sure you tested this right, it's 200Mbit guaranteed and I've never seen it dip below 350Mbit and thats probably the test server throttling it).