Did you try the violent way? https://rog.asus.com/forum/showthread.php?99490-Flash-any-most-Asus-motherboard-Bios-in-DOS-with-USB...
You may reenter your MAC address afterwards with eeupdate.exe so i advice to write it down before. https://rog.asus.com/forum/showthread.php?100441-Update-microcode-for-Spectre/page2#post709330
0607 and 0606 still use microcode 7C for my 8700k.
I tried the beta 5605 one day and write performance was good. They use microcode 6E in this version.
It is a shame a new 8700k coffee lake running 3200 CL14 RAM feels sometimes slower and more hiccuped compared to an old z77 3570k DDR3 1866.
I did build my system the day BIOS 0606 came out. If i had known what a performance disaster the Intel spectre bug was i had surely decided against a new Intel system. Intel internally did long know about it and fooled us. More as 30% performance hit for a RAMdisk alone for the Spectre fix.
btw. the PRIME Z370-A for overclocking isn't the very best choice. VR thermal throttling in a good ventilated case for Prime95 with AVX@6x4.6GHz 1.168V is not exactly a masterpiece. 60% minimum for a DC fan...
You did a nice writeup.
The overclock is 100% solid with this board since i added a tiny bit of more voltage after µC 84.
About Microsoft enabling the Spectre 4 patch by default i had the same theory as you because the last big update saw a system with old µC.
I am not so sure. It may be they let it disabled due to the additional performance hit and because intel claims this vulnerability is hard to use.
PS C:\WINDOWS\system32> Get-SpeculationControlSettings
Speculation control settings for CVE-2017-5715 [branch target injection]
For more information about the output below, please refer to https://support.microsoft.com/en-in/help/4074629
Hardware support for branch target injection mitigation is present: True
Windows OS support for branch target injection mitigation is present: True
Windows OS support for branch target injection mitigation is enabled: True
Speculation control settings for CVE-2017-5754 [rogue data cache load]
Hardware requires kernel VA shadowing: True
Windows OS support for kernel VA shadow is present: True
Windows OS support for kernel VA shadow is enabled: True
Windows OS support for PCID performance optimization is enabled: True [not required for security]
Speculation control settings for CVE-2018-3639 [speculative store bypass]
Hardware is vulnerable to speculative store bypass: True
Hardware support for speculative store bypass mitigation is present: True
Windows OS support for speculative store bypass mitigation is present: True
Windows OS support for speculative store bypass mitigation is enabled system-wide: False
BTIHardwarePresent : True
BTIWindowsSupportPresent : True
BTIWindowsSupportEnabled : True
BTIDisabledBySystemPolicy : False
BTIDisabledByNoHardwareSupport : False
KVAShadowRequired : True
KVAShadowWindowsSupportPresent : True
KVAShadowWindowsSupportEnabled : True
KVAShadowPcidEnabled : True
SSBDWindowsSupportPresent : True
SSBDHardwareVulnerable : True
SSBDHardwarePresent : True
SSBDWindowsSupportEnabledSystemWide : False
The Intel VGA GOP 1080 driver is newer if i remember right. It may fix problems with the new 144Hz monitors Nvidia lately also fixed in GOP ROM!?