Have you tried updating your Ethernet drivers?
I had a lot of issues late last year and the issues always occurred after downloading. Tried everything, but upgrading network drivers worked a treat.
I actually just updated my Ethernet drivers about two hours ago, haha! Saw some new drivers were released less than a week ago. The download speeds to Intel's site were fortunately fantastic. 56 MB download and it appeared to finish near-instantaneously.
I don't think this will help performance at all, but I certainly won't complain if it does. :)