Undercooking the core, and overclocking the HBM memory. Is that so hard to read it from my post, where I specifically pointed it, in the post you quoted? Power consumption goes down very much from down clocking the core on AMD GPUs, however, oc on Memory does not affect the power consumption in such way, as core does.
The numbers are promising, because the bigger gains are from Overclocking the Memory, than from overclocking the core. The only problem is this - from Memory bandwidth Pro apps are not benefiting as much as games. Thats what makes me slightly apprehensive for it, because Im not sure in this case Apple would consider running HBM on 640 GB/s even if it would not change the thermal envelope at all.
But that is only theory, so far.