A little over a month ago I made a video about my experience on using a 9900K in a Z370. More specifically I used my Gaming 7 as it has a very good 8+2 VRM.
The poor design of the VRM heatsink made the VRM want to boil water. I got around this by modding some old Heatkiller VRM blocks that I got on clearance ~$20 IIRC, then placed them on my board. The temps were a lot better. I did notice a couple other issues. I wasn't to happy using Prime95 and it seems like a lot of people have moved away from that or use it with AVX disabled.
I did have to restart some of my stress tests as all of my Gigabyte temp sensors would wig out and show all the same readings. Never found out why. I also came back to Prime95 and had my system power off as soon as I started a test a couple of the times I started it. I haven't touched Prime95 since.
I haven't had any issues with the system and it is running stable at 5Ghz @ 1.29v and no AVX offset. I stress tested it w/ multiple 4 hour runs of Realbench. I had some good runs at 1.285, though I would get an error on occasion.
I am curious what others have experienced.