Thank you for the reply. I have order both and will check if the D15 will fit in the build. I am using the Antec P101 case, a Gigabyte Designare MB, Corsair LPX RAM, and a ZOTAC 2 fan 2060 graphics card.I run i7 8086K oced on 5ghz 1.28V with this cooler. CPU temp in Prime 95 26.6 small ffts test is 80°C with 21°C ambient temperature. And my idle temps are 35 - 40 °C. So in my opinion this cooler will be enough for i9 9900K. But I think noctua nh-D15 would propably be better for you, but it is also much bigger.