What fraction of the speed of light are electrons moving at in the most advanced silicon chip we have? Trying to understand how much speed is left on the table for us to pick up in serial processing?
They don't move at a constant speed like say in a conductor (which isn't the case either because electric field causes resistance e.g. eddy currents, but lets say a super-conductor)
You have quite a few concepts with semiconductors primarily saturation velocity (which in most cases is the peak velocity, but not necessarily attained in actual operation) which is also affected by the drift velocity due to any electric fields in your components.
https://en.wikipedia.org/wiki/Saturation_velocity
Light speed in vacuum is 29979245800 cm/s Saturation velocity in Si based SC is 10000000 cm/s
So there's quite a bit of difference there ;)
Also because light has much more shorter wavelength than "electricity" electromagnetic waves in conductors (kilometers vs nano-meters) you can have a much higher throughput with light even if you use it to replace the carrier wires in electronics (which is what Intel is working on they want to keep electronic switching but make all carriers photonic).