Huh, but then I'm pretty sure that there are some paths inside the CPU die that are long enough that speed of light is a consideration at these frequencies. Must require a lot of smart people to design these things, yet it only takes a bunch of junior developers to bog them down.
There is indeed the speed of propagation of electric potential taken into account, that is, how long it takes for the input of a logical gate or a logical subsystem to produce the output (that involves the propagation of electric potential through the chip's conductors). If your clock is too fast for the size of your subsystem, the result will not be correct at the output before the next cycle begins, so your system will just be bogus.
