i did music last year and got a band 5, i remember i did 3 classical pieces and one modern. the examiners dont mind what you pick as long as they fit into the corresponding topics that you choose. i did Beethoven's Moonlight Sonata which was my strongest piece and that was for 'instrument and its repertoire', and for '21st century music' i did a piece called Tennessee, its from Pearl Harbor. doesn't have to be too technical, the examiners dont primarily focus on technicality. i remember lost marks in my half yearly for lack of dynamics and not generating the "feel" of the song, or so they put it. best thing to do is pick a piece you enjoy playing that you know you'll do well in.