Hi! Just a quick note about USB3 on Z68 (although my mobo is not the exact same as yours): you can read everywhere that it's not working any more past 10.9 and I have been using it very partially and had issues with my trials on 10.13 and 10.14... until very recently, when I accidentally found a fix!
I have not tested speed, but at least ports are working without any error and not only with devices connected at boot, as it was before.
While I keep using GenericUSBXHCI.kext in 10.11, CalDigitFastIO.kext + CalDigitUSBxHCI.kext are best suited for 10.13/10.14 (and maybe 10.15?)
What fixed my issues: adding EmuVariableUefi.efi in Clover drivers (no more error message) and checking ACPI/DSDT/Fixes/FixShutdown (that you already checked).
I can't try it on 10.15, though, but if you want to try... ;-)
Side note based on my trials:
- ACPI XHC patches are useless
- I'm not absolutely sure, but I seem to remember that the External Icons Patch is useless in 10.14 and maybe 10.13 too (but still needed in 10.11)
- removing AudioDxe.efi, DataHubDxe.efi, and SMCHelper.efi gains a considerable amount of boot time without any side effect here
- I had a very long boot time with recent versions of AppleALC.kext (post 1.2.8) until
I found a fix recently too.
Hope this might help/inspire you.