If I recall correctly, Anandtech's review of the X8 (and Nexus 7 2013) seemed to indicate that one of the weaknesses of the overclocked S600 (such as in the S4) when compared to the X8 version of the S600 was that the S600 was not consistently running at stride and it wasn't as adept at dynamically distributing tasks across cores.
Essentially, the Moto X quickly gets into it's green zone and stays there, while the S4 and One ramp up, ramp down, ramp up, ramp down, etc losing a lot of efficiency and, in the case of the higher clocked S4, creating a much greater fluctuation and prompting the inconsistent "stuttering" that people complain about. Basically, the third and fourth cores in the S600 create artifical limits on the productivity of the first two cores.
I don't know off the top of my head if this was solved in the S800. In the Moto X, the first core is almost always running at top speed, while the second core ramps up and down between 1GHz and 1.7GHz, with an affinity towards the top end.