yea, 4 is good. For me, i'd do the 4 i listed as my preference because i know and share the ideas (as they say, you can only sell what you yourself have bought).
When it comes down to it, know all the speeches on a general level. If they specify on 1 speech, it is normally a discuss question, which is open ended. You don't need to focus on that speech for the whole question, just some way through, like the BEGINING of the discussion (Note these are words from my teacher, cause it came up in class). Start off with it, the general knowledge of the speech will be enough to establish grounds to move into the speeches you are more familiar with.