I can't find anything that specifically elucidates the number of concurrent connections that are reasonable - nor can I find any treatises or research on this topic.
The boss says "The server needs to handle 50,000 concurrent users - so measure with 50,000 concurrent connections."
Then I see in at least one popular blog that measuring 50 concurrent connections is equivalent to being Slashdotted or Farked.
What are the numbers? What is reasonable? What isn't? How do the concurrent connections translate to number of users online at any given time?