Hey, i just built one. Its a z390 ultra with a 9700k. worked easy. I was able to take my old drive with sierra on it and plug it in. It wouldent boot on its own but it did with a mojave install usb. after that i just swaped the efi's and bang, up and running. had to mess with ssdt and audio for a bit but its up without any real trouble. Ive read a bunch of people doing fresh installs with hs and mojave so im positive it will work for you. although, im a little dissapointed overall... i had a 4790k that had been golden for a long time, never had problems and she blazed. for the money and features, this is a little less performance than i was hoping for. getting about 1600 in cinebench. it runs a couple degrees cooler at idle but as soon as you run cinebench at 5ghz, its up in the 90's. (i have a water cooler) i could oc my 4790k to 4.8 and it wouldn't get that hot, maybe just hit low 70s. and my 4790 score was 900's. so i was kind of expecting at least double with the 9700k.. overall the z390 board is really nice to look at and has nvme and thunderbolt ability my old board lacked. once it get it golden ill put the efi and ssdt's up for anyone who needs them. still working on sleep issues and at the moment and using voodoohda for sound. kindof wish i went with a 7700k and saved some $$ or waited another year or so to see whats coming down the line because the 4790 was still perfect....good luck!
