I suppose I'll start integrity checking some of my equipment. The route from this single to my bitcoind is windows client -> router -> switch -> windows host. I am thinking the switch is perhaps seeing the end of its days if it does not result as a bug. But I never really noticed any performance problems with anything... I could perhaps try downloading something that would max my bandwidth on the bitcoind machine, or comparing speedtest results between it and my machine that's not behind the switch.

Sorry, not related to cgminer, but my fingers are moving on their own...