Yeah.. the one PC with it dieing.. may be something still on that PC..
I have seen it ocasionally.. between specific switches/routers and network cards.. that it is TRYING to link at say gigabit, but then fails/has those chokes.. force drop it to 100.. works fine.. but your chokiing your potential max speed then.. something in the way the two units talk/handshake
It does sound though in general.. that something may be up with your connection.. (regards to the speeds)
Mine with express (25/2) when you run it, will SPIKE to 40+ at the begining.. then drop down..and usually ends up between 25-29 for the download... takes a bit, but then the upload test runs, and i get the 2.