Can you explain more about the voltage/clock band please? Do you mean that they are very energy inefficient?
Basically, power usage increases quadradicaly with clockspeed. Running a little faster takes a lot more power.
Nvidia runs GPUs smaller than an Apple M1 Ultra at 250-450W. Thats crazy for a single chip! They could sacrifice a tiny bit of performance and run with much less power... But they don't.
The Cerebras CS2, for reference, has a much lower power density and runs more efficiently. Unfortunately most other AI hardware is pretty hotly clocked at the moment.