I used a 3570k until pretty recently. I switched to an R7 2700X. The performance of individual cores between the two doesn't actually feel too different. The difference only really shows up when doing something where the 3570k runs out of threads/cores. In software development work I sometimes see the 2700X go a bit crazy, like compiling some large program that might have took a minute on the 3570k is done in ten seconds on the 2700X.
This Turbo voltage thing is something that's only on ASRock boards. It wasn't a setting on the boards from the other manufacturers. You need to keep that in mind when you check out what other people write about their overclocking: they never saw that Turbo voltage thing, they only had the normal offset voltage setting. When you see people talk about offset voltage, you should translate that in your mind into the Turbo voltage setting. The LLC setting is also something that's confusing when reading what other people write. On ASUS boards, the LLC levels work exactly reversed: on your board LLC 1 is the highest setting, but on ASUS the "1" is the lowest setting. The different boards also have a different amount of LLC levels. Some might for example have 5 and others might have 7. What "LLC 3" then means is a bit different.
Windows can set the CPU to a reduced speed if there's nothing much to do, like when you do boring stuff at the desktop. At that reduced speed, the Turbo voltage is not used, only the normal offset voltage setting is used.
When the CPU is set to run at its normal speed by Windows, then Turbo Boost is active. Your Turbo voltage setting will then get used. The offset voltage setting is also used at the same time, the two settings add up.
There's another thing that can happen in theory (but won't because you seem to be careful and measure things): when your CPU is running at its normal speed and it overheats and hits 105°C, then it will disable Turbo Boost and drop down to its 3.4GHz base clock speed.
I originally thought it's fine to get aggressive with LLC because I thought you can use lower voltage like that, but later learned that it's not good to use the most aggressive LLC setting(s) of the board. There's spikes in the voltage that are too short to show up in measurements. Those spikes are more extreme when using the most aggressive LLC levels and that's where my "you can use lower voltage" idea was wrong because the voltage spikes make things harder to get stable. In reality the voltage in a heavy stress test can be lower and more stable with a less aggressive LLC setting and its larger voltage droop. It's perhaps better to judge things through the temperature in stress tests instead of the voltage numbers. See also what
Something you should check out are "WHEA" warnings/errors in the Windows Event Viewer in the "Administrative Events" list. Those would show up for me on my 3570K more easily than errors in prime95. When there were WHEA events, that always meant that the overclock wasn't quite stable. The WHEA events always went away after increasing voltage enough. Sometimes it took quite a bit of an increase to make the WHEA events to go away, like for example +0.02V more voltage. About how that relates to prime95 errors or other crashes: there was always some rare crash/error if I still had WHEA events show up, like an error in prime95 that only showed up after 20 hours of prime95.
Those WHEA events could be quite rare, like only show up once every two weeks, so it was good to look for them regularly. In the Windows Event Viewer, it's possible to set up rules for when an event happens. There's guides somewhere about how to use that to open a window with a message.
The full meaning of "WHEA" is "Windows Hardware Error Architecture".