How to get better performance without going outside specifications
Under load: 3.9Ghz Vcore=1.3875
Idle: 1.4Ghz Vcore 0.8750v
Idle Boost: 4.2Ghz Vcore=1.425v
Note that under load the CPU does not use boost. Only from idle for short durations will you ever get 4.2Ghz clock.
Let us fix that.
In your BIOS,
Disable ‘Core Performance Boost’
Change your CPU clock ratio to 21 = 4.2Ghz
Set CPU Vcore to ‘normal’
Set Dynamic Vcore to +0.0125
Now your running at 4.2Ghz with Vcore 1.404v, under load, with lower voltage and temperatures than stock 4.2Ghz Vcore 1.425v on rare boost. On idle you still get 1.4Ghz clock at a slightly increased 0.880v Vcore. A non issue.
Over 12 hours at 100% CPU usage gave CPU temp 49C, with MB VRM of 72C. ~2C higher than stock settings at 3.9Ghz for the same 12 hours.
Simply setting multiplier to 4.2Ghz would have the CPU running at 4.2Ghz at 1.425v and temps approach 55C MB/85C VRM fast, due to the 1.425v auto setting.
If you do want to go over specification then with this method you could raise to 4.3Ghz or 4.4Ghz while only raising Dynamic Vcore up to the rated 1.425V. I will leave that to you, but keep an eye on CPU temp and MB VRM temps. CPU should not go more than 60C and MB VRM no more than ~90C.
MAX VRM temp for my MB is rated at 110C before throttling.