@igormp So, if I remove all power limits in BIOS and make sure I have enough thermal dissipation, I can get EXACTLY the same frequency on all cores that I would get on a single core, or is there going to be something hold be a little behind?
Without an overclock, you won't see the max boost frequency on all cores. Intel used to actually be open about this and publish what were called "Boost Tables" that told you exactly what clockspeed to expect when having 1, 2, 3, etc. cores under load. Here's an old example from the first gen core series:
So the i7 870 will only boost to its rated 3.6GHz max if a single core is in use. If 3 or 4 cores are in use, it will only boost to 3.2GHz. All Intel CPUs still have a boost table to this day, and you can actually find it via software like Intel XTU, but Intel no longer makes the information easily publicly available.
For AMD, it's more complicated, and the exact way they determine this is not publicly known - at least, I've never seen it published anyware. They don't have a basic Boost Table like Intel does, and instead use an algorithm based on temperature, power, and current. But the result is similar: In practice, you're ever going to see the max rated boost clock on an all core load, even if you remove power limits.