I dont know the prices in the US but here in the netherlands the PS4 Slim is cheaper then the X1 S and the PS4 Pro is down to 369,-
Even tough the Xbox has deffenitely sold better recently, with forza and gears, with the prices being what they are and the extra value of the Pro I am quite certain sony should have November and December, I am expecting November to be the bigger gap because of the kick-in of the PS4 Pro pre orders.
it all really depends if the Pro keeps selling or its a one time boost.
Twitter @CyberMalistix