I'd tell you to add something from Boulez just because he's one of my favourite composers, but I'm worried that you might alienate some people with it, since Boulez's music in all its beauty is so icy cold and jagged...but I must ask what piece of his you were considering playing, i think the 2nd movement of his sonata #2 might be the most accessible, it's kind of like the slow movement of Beethoven's #29, but nevermind, it's too long...hmmm perhaps the 1st movement of sonata #1 then? I don't know, I still think a lot of people have a natural aversion to Boulez which might hurt your chances in the competition
but Schönberg is probably my very favourite composer, so I must say that I would play anything of his other than something from the suite (just happens to be one of my least fav. pieces by him), I'd say one the 5 pieces or one of the 2 pieces, his op. 11 is great but I think it must function as a whole and the 6 little pieces are too easy........... the concerto movement might be really awesome since it's such a brilliant piece, I need to listen to it more though....I'll try to listen to these pieces more tonight so I may be able to give you more ideas