https://www.techpowerup.com/248595/gigabyte-z390-oc-guide-suggests-intel-9000-series-processors-will-run-hot-even-with-custom-watercooling
 
Z390 overclocking (OC) guide specific to their AORUS-branded motherboards: "As you can tell from the last screenshots, the CPU temperature of the i9-9900k is quite high. This is something that we've noticed on almost all the processors. For this reason we suggest you to use a custom water-cooling and adjust the TjMAX Temperature to 110°C." The quote references their guide to achieve a stable 5 GHz overclock on all cores on the Core i9-9900K, which was cooled via a custom watercooled setup and a Vcore ranging from 1.3-1.4 V. GIGABYTE's internal testing thus indicates that these higher end, unlocked 9000-series CPUs will run incredibly hot if you wish to push them. So if you are thinking of pushing these to 5GHZ make absolutely sure your cooling is maximum.