Only two casts of Kozilek, the Great Distortion so far. First time, he drew three cards and got countered. Second time, he drew five and countered a Swords to Plowshares, prompting a concession. Not enough information to really say either way yet.
Warping is indeed one of the best card for this deck. How many copies do you play? I'm currently blocked on 2....I'd like to play 3 of them (also 4 if I had more room) but having already 1 pyroclasm and 2 kozilek's return limit the need of the first warping option.