IBM had 5GHZ in 2014. [1] Clock speed is not a measure of performance alone.
Besides, most of the work in reaching a certain clock speed or target can be owed to the foundry (in this case TSMC which is world-leading, certainly beating Intel on most metrics at the moment.)
Comparing to the over-tuned enthusiast SKU of 2018 is not a fair comparison for either.
Also 600W is not impossible to cool, there are GPUs at that level of power for a while now.
Besides, most of the work in reaching a certain clock speed or target can be owed to the foundry (in this case TSMC which is world-leading, certainly beating Intel on most metrics at the moment.)
Comparing to the over-tuned enthusiast SKU of 2018 is not a fair comparison for either. Also 600W is not impossible to cool, there are GPUs at that level of power for a while now.
[1] https://en.wikipedia.org/wiki/POWER8