feedmeink: I agree with all you said. AVX takes a larger setback than in 4- or 6-core i7, minimum 3x for AVX and 5x for AVX512. I looked at y-Cruncher (quite sensitive to memory tuning, CPU speed and stabilty, and to the use of AVX) scores. On water, with AVX at 4.5GHz compared to very little AVX using Sandybridge workload at 4.9GHz -- with AVX ran in half the time even with slower clock. The setback earns its keep to retain the efficiency of AVX instructions.
I also agree with what you say about core volts, but please tell me that 1.7v is a typo. I'd prefer 1.17v. Under dry ice, I have had the courage to go to 1.325Vcore to get over 5GHz clock under benchmark loads.
I didn't mention that my RAM tuning was done with 4400 C19 G.Skill sticks. Some of the blame for limiting those to 4200 or 4000 has to fall at the feet of the motherboard as shown by the difference between motherboards and that my 7820K also tuned around 4200 on the R6A with the same RAMs. Nonetheless, the HCC CPUs don't seem able to get to the 4400 that 8700K, 8600K, 7700K have been able to do.
My testbench is equipped with a water chiller. I try to do longer tuning sessions with water temperature just above the dew point to eliminate condensation. The chiller has a tough time keeping up with the total power thrown off by the 7980XE in multicore work. It handles a 6950K or 7820K well enough, so I know it's capability is as designed for a 15C temperature drop at around 120watts, but not at 225watts. I agree that no air cooling nor any AIO water loop would be able to cool this many cores.