This one seems that it wouldn’t help but I have to post a quick note about Cat6 Cables verses Cat 5/5e cables.
I have been fighting with a server that has a Gb network card attached to a Gb switch barely reaching 100Mb/sec network speeds. As it turned out the cables that were connecting the server to the switch were older Cat5e network cables. Although the Cat 5e cables are rated for Gb speeds, apparently because the cables were so old or possibly had minor unseen damage they were not sustaining the higher speeds.
After the switch to new CAT6 cable the network speed came back to what it was supposed to be.
I realize that this fix will not work for everyone as there are many causes of slow network speeds but ItFixed it for me. It may be worth looking as the simpler fixes before pulling out any hair.