Shinobi-san on 29 January 2014
It's quite simple really. MS prioritized the bundling of kinetic. So in order to keep the total price of the x1 down and fit kinetic, they needed to make sacrifices on the rest of the hardware. This resulted in MS choosing a gpu equivalent to a hd7770.
Sony on the other hand chose not to bundle their camera and focus on the core components. This resulted in a much better gpu and better memory for gaming. The biggest contributor to the power difference though is the gpu...which is equivalent to a HD7850 more or less.
Have a look at the benchmarks between those two gpus and it pretty much says everything.
