My guess would be the IGPU is the limit as that shares the same package power as the CPU so it might be the case that the IGPU is power throttling in favour of the CPU since generally you should be using a discrete GPU instead of relying on an IGPU for workloads like complicated games.
Disabling turbo is correct since the CPU is least efficient at the highest frequencies. Turbo is effectively a factory overclock so is very inefficient. High end consumer CPUs often operate below turbo frequency under all core workloads because of power limits. Disabling turbo will assure the CPU does not use power inefficiently that could be going to your IGPU instead.
Disabling AVX is a bad idea. AVX as an instruction set is power efficient. Claims of it being less power efficient come from a micro architecture point of view where the transistor leakage power could be used else where or not exist at all if the CPU did not implement AVX. Since your CPU has AVX support (the transistors physically exist already), it has the leakage no matter what so disabling it is pointless and if anything is likely to harm your CPU efficiency by not allowing AVX instructions to be used where they would benefit.