The vs. Aronian games will probably be the only telling indication of his form/preparation ... and even then, it will be a factor of "how sloppy is he NOW compared to the last WCh or even in Candidates" rather than how good is he playing. (Highly doubt he'll pull a Fabiano and play a near-flawless wipe-the-competition type tournament)
Though how consistent he is now might indicate if he's been training to play long-haul drag-it-out grinding games better than he's ever done before.
Anand starts well beating ponomariov. He seems to be in good form.Lets hope for a good fight between him and carlsen.