Sorry for late reply, just travelling back from Macau.
Result basically same as iMac14,x/15,x, tested with HSW G1840 + RX460.
No matter SMBIOS iMac14,x/15,x or iMacPro1,1, all without built-in frequency vector table in X86PlatformPlugin info.plist, just common XCPM control.
If want better CPU PM or PM not limited by SMBIOSs, try inject frequency vector table to X86PlatformPlugin info.plist, download CPUFriend from below link and place it to CLOVER/kexts/Other, copy attached frequency data sample to CLOVER/ACPI/patched.
See below link for detail, need lilu.kext
Dynamic macOS CPU power management data injection. Contribute to acidanthera/CPUFriend development by creating an account on GitHub.
github.com
ssdt-3300.aml offset at 3.3 GHz, suitable for HSW/SKL/KBL CPU frequency from 2.9 GHz to 3.7 GHz.
ssdt-3500.aml offset at 3.5 GHz, suitable for HSW/SKL/KBL CPU frequency from 3.1 GHz to 3.9 GHz.