Please bear in mind that Intel does not provide assistance for overclocking. I would recommend waiting for another community member to post similar experience.
Doubling the core frequency increases the heat loss by the factor 4.
I really can´t recommend it.
To improve the system performance, check the Bios settings: virtualization ON.
Can you post the hardware config of your computer?
It is possible to improve the system performance in many different ways.
E.g.: increase RAM size, add SSD, add better graphics card.
ArminM is correct. Going to 4.2 means a 0.4 increase from the default maximum, which is a lot. ArminM's last sentence is good advice and I would add a good aftermarket cooler from Noctua. Go into BIOS and enter F9 which will reset all values to default. If you continue to use XTU, only bump it up 0.1 and use it for a long time to see if it is stable, but only after adding a better cooler. Heat is not your friend.
To be clear...
We had this running for over one day at 4.2ghz and the temp did not go past 55 C.
Something happened that reset the Extreme Tuning Utility to defaults, now settings that were available are now greyed out including the multiplier.
Intel Xeon does not allow overclock, it seems there is a glitch in XTU, which did not check CPU capability before it run. You might get lucky when running XTU and overclock CPU on first boot.
This is incorrect. I own this processor and can confirm it's unlocked.
What's the motherboard? And what's the XTU version?
It is an Intel made board built for HP and the lates version of XTU.