In this respect... the Mephisto RISC 1MB and Mephisto RISC 2 modules come to mind. The clock frequency of the ARM (around 14 MHz) is very inaccurate, because the oscillator is adjusted with a variable resistor!! (small black potentiometer located near the EDGE connector).

And of course all those chess computers with Hitachi HD6301V1, HD6301X0, HD6301Y0, etc. in which the clock signal is not generated with a quartz crystal but with an LC oscillator circuit.

But in both cases I think that different results would be obtained in blitz games.