/defxor
Anecdote: At home I have an 1987 Atari ST, including a SM124 monochrome monitor and an RLL MFM 30GB hard disk in working condition. The picture quality is slightly unstable, most likely due to the caps in the PSU needing to be exchanged.
Mining wreaks havoc on gates, whether it's a CPU, GPU, FPGA, or ASIC. Mining absolutely hammers it, 24/7/365. Mining will wear out any device far faster than normal usage.
Actually if you know how hardware functions, a 1GHz CPU will always switch the gates at that frequency when the PC is powered on, once the operating system is loaded it will send a continuous off command to stop the switching of the unused gates when there is nothing to process. So really it makes no difference whether the CPU is processing or is in pre-OS state and switching anyway.
Excess heat and current is what degrades the silicon.