Hi Ari,
According to this question, seems that you can select different frequency of crystal.(for example: 16MHz)
Here are two clocks_source which generat maximum CPU and peripherals clock for 12MHz and 16MHz crystal.


The maximum CPU and peripherals clock for 8MHz crystal can be found in 'MKV58, Need clock_config.c for a 8 MHZ external crystal'.
Best Regards,
Robin
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