May want to disable IPv6 if you can... SE is still using V4 addresses, so you are injecting a slight bit of lag in there. While it may typically only be on the order of up to 10ms or 30ms at worst, it is also an additional layer of translation that may bring it's own weirdness to your environment, and you would need to track down if it is happening at the Windows stack, the router, your modem, or somewhere further up the chain.