Personally, I like the Bach-Busoni and Schubert Impromptu, but I wouldn't recommend doing the two Beethoven sonatas like that---or, for that matter, the Schubert 960. I would consider dropping the Op. 90, playing the op. 109 in its spot, and then finding some later Romantic or 20th Century pieces to play in the beginning of the second half before the Wanderer Fantasy. Of course, if you wanted to remain a little more in the "earlier" times, you could also look into a Mozart or Haydn sonata.
What else is in your repertoire? Or, what else are you interested in playing that you could learn by December?