Transfer speeds only around 50mbps over the network.

I am trying to transfer a very large (300gb) file over my network, but the speeds seem to be capped at about 50mbps, they are both running short Cat5e cables and are right next to each other plugged into a Gigabit switch, they both have Gigabit network cards, does anyone know why this could be happening? Thanks

What protocol are you using? Can you achieve higher throughput using any other client with the same protocol?