Keep in mind though that not all emulation has accurate timing. There are issues with so-called waitstates in several of the drivers, such as Mephisto Glasgow, the emulator will be faster (play a bit stronger) than the real thing. It's fine when you're just playing, but annoying if you want to do ELO tests.

Or emulation can run too slow due to missing emulation of CPU cache and whatnot, like Fidelity EAG V11 or Saitek Sparc.