Network crashes under heavy load

[Nathen <n147258369@googlemail.com>]

For some reason my server stops responding to network traffic (shares
go offline, no response to SSH or ping, etc) after heavy load -
transferring large amounts of data via Samba or running several iperf
benchmarks causes it, however the system still responds to the power
button so shuts down when it's pressed. I'm using an Intel D510MO
board with Realtek 8111DL network controller which I'm guessing has
something to do with it, I could be wrong. I think it might be a bug
but I thought it best to ask here first.
Thanks. :)