For the sake of argument, consider 1) a player...we'll call him Player 1...who is so far away from the spawn chunks that the spawn chunks are a non-issue, and 2) the server that Player 1 plays on has its view distance set to 10.
So if Player 1 is standing at x = 90 and z = 90, this puts him roughly in the center of chunk 5,5. How far would this player have to walk to cause chunk 5,5 to unload? Suppose he walks east. Would he have to walk greater than 10 chunks east? Chunk 15,5 is the tenth chunk east of 5,5, so if Player 1 is still inside chunk 15,5 then chunk 5,5 should still be loaded, right? But as soon as Player 1 walk into chunk 16,5, then chunk 5,5 will unload, right?
This is assuming a 10 chunk radius around the player stays loaded. Is the radius spherical?
Is there a test I can do to find the spot where a particular chunk will unload once the right distance away has been reached?