OK, as of right now, I can't suggest MSI MEG x399 AT ALL. And I am not sure I can suggest buying 2990WX until there is better board out there.
There is zero bios support. Last public one was 6 weeks ago ! I have big troubles with repeated boot into microcache loading with no apparent solution.
Fun fact: The recent Windows update came with microcode (yup, the same one in July) and capped the turbos severly from 4.0Ghz to 3.5Ghz. Uninstalling the patch and deleting mcupdate dlls (shitty procedure as you need to disable trustedinstaller in Win10) did not return anything. Manually forcing higher turbos (OC) in uefi only causes another mysterious boot issue, C5. Yup, there is no such thing as C5 Q-code in manual as of now.
You guys have no idea how disappointed I am in this. I've no idea what to actually do. Should I replace the board with some basic stuff like Taichi until x499 is here after winter ? Is x499 even coming ? Or wait who knows how long until MSI bothers to actually publish new uefi fix.