Try using a different port for the other LW. Since it's probably set to UPnP, you can try putting in the port number & hope it doesn't change, else, set to manual port forward (however that will probably leave the router's nat closed port.) Perhaps safest way is to port foward a port for one, upnp for the other. Just a thought.

Also keep in mind those suggestions you tried, such things as disabling OOB & performance options may just make that much of a difference initially after trying the above with port setting.