I found only one old topic on this question, which got very little attention (and I don't agree with the conclusion that the two posters there came to).
The question is how (if at all) do the Performing Combatant and Masterful Display feats interact?
My interpretation is that you make a performance check with Performing Combatant (choosing Masterful Display as your performance feat), and then select two other performance feats as per Masterful Display. If you succeed on your Performing Combatant check (which would gain the +2 from Masterful Display if applicable), you gain the full effect of the two performance feats you selected with Masterful Display.
The interpretation that the posters in the previous topic came to was that you make a performance check with Performing Combatant (choosing Masterful Display as your performance feat), and then select two other performance feats as per Masterful Display. If you succeed on your Performing Combatant check (which would gain no bonus) absolutely nothing happens, but you are then allowed to make Masterful Display performance checks at any time during the remainder of combat to gain the benefits of that feat, though it can only be applied to the two performance feats you selected for your original Performing Combatant check.
What do others think?
The question is how (if at all) do the Performing Combatant and Masterful Display feats interact?
Performing Combatant (Combat) - Benefit: You can make performance combat checks in any combat. When making a performance check outside of performance combat, you can pick a single performance feat to use. You automatically gain any bonus on the performance combat check the feat grants, and then you make a DC 20 performance combat check. On a success, you gain the full effect of the performance feat you chose.
Masterful Display (Combat, Performance) - Benefit: Choose the effects of any two performance feats you have. When you make a performance combat check, you gain the benefits of those two feats, but you only gain a +2 bonus on the performance combat check.
So you use Performing Combatant, and choose Masterful Display as the performance feat.
If you do not choose Masterful Display as one of the two performance feats to use Masterful Display with, then you do not get any bonus on the performance combat check you're about to make as part of Performing Combatant. If you do choose Masterful Display as one of the two Masterful Display feats, then you get a +2.
So make your performance combat check, DC 20. Apply the +2 if appropriate. If you fail, nothing happens.
If you succeed, then you gain the full effect of Masterful Display.
The full effect of Masterful Display is that you gain the effect of the two feats you chose when making a performance combat check, and a +2 bonus on those checks.
If you are not making a performance combat check, then Masterful Display does nothing.
-edit-
I would not allow you to retroactively gain the effects of Masterful Display on the performance check you made to determine if you can gain the effects of Masterful Display. You would only gain those benefits on performance checks you make after the feat is 'active'.
If you do not choose Masterful Display as one of the two performance feats to use Masterful Display with, then you do not get any bonus on the performance combat check you're about to make as part of Performing Combatant. If you do choose Masterful Display as one of the two Masterful Display feats, then you get a +2.
I don't think that's how Masterful Display works. Otherwise you could choose two feats with Masterful Display; one performance and one Masterful display. With that Masterful display you could choose two more feats, another performance, and masterful display, and so on, until you're using all of the performance feats at once.
I'm guessing that RAI is that you can't select Masterful Display with Masterful Display, despite it being a performance feat. You're supposed to select two other performance feats.
The way I read the rules, the +2 that Masterful Display is referring to is for feats like Daring Display and Heroic Display. Both grant a +2 on the perform checks to make them, in addition to their other benefits. Masterful Display is saying that if you choose both of them you get all the other benefits of both, but you only get the +2 once, essentially that the bonus doesn't stack.