It really depends on the question. Some questions specifically ask for ONE related piece of material. If they do, then ONLY provide one.
Many questions will ask for TEXTS of your own choosing. If so, then it's definitely better to do two texts. You should have enough time to cover them properly. If you're only covering them briefly, you may not get across everything you have to say.
But yeh, the question usually specifies. It's a good idea to go into the exam knowing 2 pieces from the stimulus booklet (just in case) and 2 related material (also just incase lol). Good luck!