Asrock Z77 Extreme4 - d6

Serious?
A 10 year old board, and ASRock must tighten up??
If it was PITA from the start, you should have sent it back under warranty, not wait 10 years.
Regarding XMP, it is overclocking for dummies, no manufacturer guarrantees it will work.
It is a set of vallues, that is SUPPOSED to work, with all existing combinations of CPU, chipset, and motherboard on the market, it is far from optimal.
And for your Info, the memory controller is integrated in the CPU, not on the board, it runs optimal at 1066MHz
https://ark.intel.com/content/www/us/en/ark/products/52214/intel-core-i72600k-processor-8m-cache-up-to-3-80-ghz.html

Some CPU coolers go way beyond the intel specs, when it comes to the pressure, the cooler applies to the CPU / socket, and bend the CPU and socket, so much, you will get contact problems.
And it might simply be a bad CPU, there is a reason why professional overclockers, try to find the Golden Sample, that gives them enough headroom for OC
Overclocking is always a game of trial and error.
Code 55, is the memory check, code D6 means no Console output devices are found, so your graphics card, or monitor is not detected