Actually the issue you are experiencing is expected because the processor has been overclocked. The reason is because this new technology of processors has the Memory Controller Hub (MCH) inside of them, so now is the processor is the component that controls the memory. Specifically for your processor i7-2600K the MCH on it, was designed to support up to DDR3-1066/1333MHz memory at 1.5V. This information is on the following link; please check the paragraph that says memory specifications: http://ark.intel.com/products/52214/Intel-Core-i7-2600K-Processor-%288M-Cache-up-to-3_80-GHz%29
Now your memory is 1600MHz with a Serial Presence Detect (SPD) of 1333MHz, the SPD is the minimum speed that your memory is able to work, I´m just guessing this based on the situation you described that it run on auto but no with the XMP.
Running the memory with the XMP of 1600MHz you are running the memory out of specifications so you can have two possible scenarios:
- 1. The memory is downclocked by the processor in order to be able to work with it; this means that the system is not able to use your memory at 100% of capacity.
- 2. The memory force the processor to reach the speed of it, on this scenario the processor is overclocked by the memory, and this is the most dangerous scenario because eventually your processor could be damage.
In the same way these scenarios apply for the voltage. Your memory is out of specifications since the voltage of it is 1.6V, I don’t know if it has SPD voltage of 1.5V, if that is the case, the SPD voltage is fine but, when the memory gets the 1.6V with the XMP your processor is overclocked as well. To make sure about that we recommend contact the manufacturer of the memory
In this case we recommend that you use your memory within specifications, up to 1333MHz at 1.5V maximum.