There is a way to disable both Meltdown and Spectre patches via registry in Windows 10, but does it have a performance-enhancing effect if BIOS CPU Microcode is also patched for Spectre and Meltdown vulnerabilities?
To disable Meltdown and Spectre patches in Windows 10, paste this into txt file, save as reg and merge:
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management]
"FeatureSettingsOverride"=dword:00000003
"FeatureSettingsOverrideMask"=dword:00000003