I think the 7.5 million number you used for the XB1 is wrong, you read too much on Ars's shitty gaming section.
if anything it's at 6.5 and this is a fair assessment.
But please, maybe I am wrong about the XB1 number, can you provide a reasonable source (the math in the Ars article did not add up, even as a "ball park" number it makes no sense).