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Processors can adjust their frequency based on a number of factors such as temperature, number of active cores, type of workload, among others. Even if processors have different Thermal Design Power (TDP), it usually provides information that allows you to keep optimal operation and long-term reliability of the processor and choose the right cooling system.
Keep in mind that processors use a number of technologies such as Intel® Turbo Boost Technology that automatically improve energy efficiency and maximize frequency as well, but you cannot control this behavior. Now, because the Intel® Core™ i7-8700K Processor is unlocked, you may see considerable difference in power consumption and data processing for some applications. However, as I stated before, a lower TDP will not affect the processor unless a proper cooling system is used.
To get additional information about the processors, you can also click on the link below to compare both processors.
-Compare Intel® Products