Qualcomm itself confirmed its Snapdragon 800 is what will be powering the Lumia 1520 phablet, responding to a tweet, then quickly retracted the statement, realizing some non-disclosure agreements are still in place before the official unveiling, but the cat is out of the bag...
Source: http://www.phonearena.com/news/Qualcomm-tweets-Nokia-Lumia-1520-phablet-will-sport-Snapdragon-800_id47611
Source: http://www.phonearena.com/news/Qualcomm-tweets-Nokia-Lumia-1520-phablet-will-sport-Snapdragon-800_id47611