Overclocking was held back by temperatures a lot. Even with 240 mm AIO watercooling, we could barely tame the temperatures. We had to keep dropping voltages until we ended up at only 1.225 V, which of course means high clocks were out of the question.
At that voltage setting, our maximum manual overclock was 4.0 GHz on all cores, which is significantly lower than the maximum boost frequency of the processor (4.6 GHz). As our performance numbers show, the manual overclock can only shine in specific applications that fully load all cores, in which the processor at stock would dial down its clocks automatically.