This message was posted on behalf of Intel Corporation
In this case, since the Intel® Turbo Boost Technology doesn't have any tools for you to customize (it is automatic), it will depend on the workload, so you will get 4.2 GHz if just one core is being used. Please check the following link for information regarding max CPU frequencies:
Intel® Core™ i7 Desktop Processor Turbo Boost Technology Frequency Table > Expand "6th Generation Intel® Core™ i7 Desktop Processors".
In regards to the following statement: "some stuttering I have recently been getting in games", can you please describe the behavior of the system?
In addition to the above information, please download and run the Intel® Processor Diagnostic Tool and provide a screenshot with the results.
Are you using an XMP profile? If yes, what is the speed of the RAM?
I am looking forward to hearing from you.