Right, downclocking is a different matter and I'm aware of the pitfalls there. As you point out, the extent of the downclocking varies based on the model - and

Right, downclocking is a different matter and I'm aware of the pitfalls there. As you point out, the extent of the downclocking varies based on the model - and also the exact "license" chosen depends not only on the instructions used, but their relative intensity (e.g., you can do a lot of 512-bit FMA instruction without suffering the slowest speeds, but once FMAs are dense enough you'll get the downclocking). FWIW, I recently tested a consumer Cannonlake chip and there is no downclocking even with heavy AVX-512: all types of tested code ran at the full turbo frequency. So it seems that not all chips will have these varying frequencies based on ISA extensions used.