For anyone curious why this doesn't translate into a 427GHz computer, light can travel about 1.4mm in one cycle at 427GHz, meaning that all synchronized components would have to be located within 1.4mm of each other. The bottleneck for processor speed became the speed of light some years ago.
The speed of light isn't directly why commercially available CPUs stopped getting faster (in terms of clock speed). That's more related to the fact that the increased transistor density and thinner gates (with more leakage) have pushed power dissipation to its limits. If we clock any faster, the CPU will burn up. That's why you can overclock if you use liquid cooling, for example.
That said, I'm sure there are fundamental limits to transistor clock speeds imposed by the speed of light. It's just not why CPUs stopped scaling around 2-4 GHz.