Overclocking on our Core i9-9900K sample using air cooling was held back by temperatures. Even though the IHS is soldered on now, heat doesn't just magically disappear. We could set a voltage offset of +50 mV, on air, while staying outside of thermal throttling, which resulted in a stable clock of 5.0 GHz on all cores.
Using a 240 mm all-in-one watercooling unit, temperatures were no longer a problem, and we could dial up the voltage. We picked +150 mV for this scenario as it's a reasonable increase that won't harm the lifetime of your processor.
Here, we reached a completely stable 5.1 GHz on all cores (even with +105 mV). While the system booted fine at 5.2 GHz, it had a tendency to crash when heavily loaded, no matter the voltage (we tried up to +250 mV), so we settled for 5.1 GHz as our stable overclock, and will include that overclock in all performance comparisons.
As mentioned before, the heatspreader is now soldered on instead of using thermal paste, which has a positive effect on temperatures. They are a few degrees Celsius better.
Power LimitSince the Intel Core i9-9900K is specified with a TDP rating of 95 watts, the BIOS is configured to automatically use that value when the processor gets installed.
We did some testing using Blender (which will load all CPU cores completely), and varied the "Turbo Power Limit" in BIOS, which controls the TDP setting of the processor. The chart's vertical axis shows how long Blender took to complete the given rendering task, and the horizontal axis shows the TDP limit we've set. The orange marker shows result at stock, with the processor's rated TDP of 95 watts.
As you can see, there's quite some performance to be gained by dialing up the power limit. The improvements are substantial until around 180 W, beyond which the processor no longer throttles and no further gains can be had.
Throttling in this context means that the processor will not boost nearly as high. Instead of 4.8 GHz all-core (180 W), it was running at around 4.1 GHz when left at stock TDP.