Don't mix memory kits. Memory kits are sold in matching kits that are designed to work together as a set. Mixing memory kits will cause stability issues or system failure
Memory kits will boot at SPD speed with BIOS settings by default with compatible hardware
For memory kits with XMP, enable the XMP/DOCP/A-XMP profile in the BIOS to achieve the memory kit's nominal potential XMP overclock speed, provided compatible hardware is used
Achieving the nominal XMP overclock speed and system stability will depend on the compatibility and capacity of the motherboard and processor used
Use that does not meet manufacturer specifications, warnings, designs, or recommendations will result in reduced speeds, system instability, or damage to the system or its components