I find it interesting when someone makes foundational improvements when using an FPGA to mimic an old CPU.

The NextZ80 is a good example. It's designed to run 4x the amount of instructions at the same clock rate as a real Z80. And you can clock it to 40MHz, so it's effectively a 160Mhz Z80...compare to a typical 4/8Mhz real Z80.

https://opencores.org/projects/nextz80

Yes, but how many programs written for the real thing have hard coded values dependent on cycle times?

Perhaps for games on a platform like the ZX Spectrum and MSX, but I suspect most of the CP/M targeted apps wouldn't care.

But how many of those systems have BIOS code that uses hard-coded timing loops to talk to devices?