Do not mix memory kits. Memory kits are sold in matched kits that are designed to run together as a set. Mixing memory kits will result in stability issues or system failure. Memory kits will boot at the SPD speed at default BIOS settings with compatible hardware. For memory kits with XMP, enable XMP/DOCP/A-XMP profile in BIOS to reach the rated potential XMP overclock speed of the memory kit, subject to the use of compatible hardware. Please refer to the "How to Enable XMP/EXPO" guide. Reaching the rated XMP overclock speed and system stability will depend on the compatibility and capability of the motherboard and CPU used. Usage in any manner inconsistent with manufacturer specifications, warnings, designs, or recommendations will result in lower speeds, system instability, or damage to the system or its components. Memory module height can be found in the FAQ, under the question "How tall are the memory modules?". For product support and related questions, please contact the G.SKILL technical support team via email. | 
