Have a look at what ThrottleStop reports for C0% when your computer is idle at the desktop with only ThrottleStop open. With a 6 core CPU, the C0% should be around 0.5% or less. That is normal. With 10 cores to share the load, less than 0.1% is possible. This is the most accurate measure of what a CPU is doing when it is idle. If your C0% is high or quite variable, your benchmark scores will suffer.
Your power limits are locked. For a short period of time, your CPU can run at up to the 154W PL2 limit. After approximately 28 seconds, the CPU will be limited to only 100W. If you do back to back benchmark tests, your second test will likely be a lot worse than your first test.
Intel says turbo boost is like water in a bath tub. If you completely drain the turbo boost tub during one benchmark test, you will have to wait for the CPU to recover. Watch the ThrottleStop reported multiplier and watch the Limit Reasons window while Cinebench testing. Do you see PL1 or PL2 throttling during this test? With locked power limits like you have, there is nothing you can do about power limit throttling. If you see some other type of throttling in Limit Reasons, post a screenshot while it is happening.
Turn on the Log File option on the main screen of ThrottleStop so you have a record of your CPU performance. Go play a game for 15 minutes or do some benchmark testing. The log file will show how your CPU is performing. Your less than great UserBenchMark score is likely because of your locked power limits and stuff running in the background that you are not aware of. Look in the Task Manager and go to the Details tab. How does that look? My computer usually shows 99% for System Idle Process. That is with multiple tabs open in Chrome, the Paint.NET program open, File Explorer open and ThrottleStop open.
You can copy and paste log file data to
www.pastebin.com
Edit - Your UserBenchMark score shows Background CPU 10%. My computer shows only 2%. That is why when I run this benchmark I get much better than average results for my CPU. Concentrating on the little things can make a big difference.