@zoomkat: I agree to a point. Like I said, mine seemed to allow at least two other connections (no response) while the w5100 did respond to the current socket/connection. That I expect. I have not tested it in a while. I think you have a couple posts in that topic where the test was done. It is 18 pages long. 
edit: zoomkat, you might be the person to test this. As I recall, you have server code that sends a page that auto-reloads every second or so. Put some delays in the server code so it takes a few seconds to upload to a client, then start about 3 computers on it. That was my test.