An 11900K can run single core tasks like Cinebench faster than an 11900F. It is Intel rated to be 100 MHz faster. When installed in the same computer with the same operating system and same background tasks running, a 11900K should be faster compared to a 11900F.
https://ark.intel.com/content/www/u...1900k-processor-16m-cache-up-to-5-30-ghz.html
https://ark.intel.com/content/www/u...1900f-processor-16m-cache-up-to-5-20-ghz.html
I would not use CPU-Z as a single core test because it fully loads two threads which fully loads and activates two separate cores. Results can vary depending on what operating system is being used and how many background tasks are running. The Cinebench single core test is a true single core test. Cinebench results tend to be very consistent. Their 100 point score is right in line with your 99 or 100 point scores when your CPU is not throttling. Without sitting with the Asus tech, it is impossible to know what BIOS settings they used.
During the Cinebench 2024 single-core test, HWinfo shows that the processor frequency can reach up to 5 GHz.
You have already seen during your testing that HWiNFO does not accurately track the CPU MHz during single core testing, especially when a CPU is throttling. Your CPU at default specs was significantly throttling. It was not until you started using ThrottleStop that the reduced MHz became obvious.
Intel individually sets the voltage curve for each CPU. Your CPU combined with your motherboard is likely setting the CPU voltage high while the 11900F that Asus tested might be setting the voltage at an average or lower than average value. This varies depending on what VID voltage table was programmed by Intel into the CPU. High default voltage is causing your CPU to VMAX and EDP throttle during single core Cinebench testing.
I would not say the processor is faulty. It is more of very poor quality than outright faulty. It is more than three years old so I am not sure if Intel would be willing to replace it or not. Probably not. There is no guarantee that a replacement processor will be any better.
Intel does not guarantee that the maximum turbo frequency will be achieved or maintained during Cinebench or any other test. It is more of a theoretical maximum.
Max Turbo Frequency is the maximum single-core frequency at which the processor is capable of operating using Intel® Turbo Boost Technology and, if present, Intel® Turbo Boost Max Technology 3.0 and Intel® Thermal Velocity Boost. Frequency is typically measured in gigahertz (GHz), or billion cycles per second.
If it was my CPU, I would continue using it as is with the reduced loadline values and any other ThrottleStop tricks that might be necessary so it can run single core tasks at its full rated speed. After a few minor tweaks, your CPU is capable of running as it was designed to run.
I always buy K series CPUs even if I do not intend to overclock. Intel bins every CPU they produce. Their best CPUs that can run reliably at low voltage are likely to become K series processors. CPUs that need more voltage to run reliably become non K series CPUs.