Obviously your RAM speed is the cause, not the sim.
XMP causing CTDs is common, particularly with certain Intel cpus like the 9700k that tend to rise very sharply in temperature. Sometimes it is better to leave the RAM running at a lower speed, and overclocking the CPU instead. You could also underclock the CPU and enable XMP. Whatever you do, you should always check stability with a program such as CPUID Powermax.