Let's see...
September will go in Sony's (PS4) favor with the Metal Gear bundling, Destiny: The Taken King bundling and pushed possibly by a couple of sleeper titles (i.e. Until Dawn, SOMA, etc...). And more than likely they will lead in the multiplatform sales this month with FIFA 16, NBA 2K16, NBA Live and Pro Evolution Soccer 2016.
October will be a toss-up between the PS4 Nathan Drake Uncharted Collection bundling and the XB1 Halo 5: Guardians bundling. The other multiplatform deal breakers that may sway potential buyers to either platform will be titles like Wasteland 2: Directors Cut, The Witcher 3: Wild Hunt - Hearts of Stone, Assassin's Creed Syndicate and possibly two other well placed titles.
November will go in Sony's favor, although Microsoft may lead in Black Friday sales. Sony's trump card will be the linking of everything Star Wars during that month, especially the PS4 Star Wars Battlefront bundling. I'm almost dead certain, the Battlefront bundling will push more than the Batman bundling that sold over 100k units and the Destiny Bundling back in September 2014, that was over 300k units sold (400-425k PS4s sold during that month). I think some people are going to underestimate the PS4 Battlefront bundling, like they did the Destiny bundling.
December, more than likely will go Microsoft. I think Microsoft will go all out that month just to save face. The only way Sony takes December will be because of a price cut. Maybe a pricecut around Black Friday during the November time-period.