It would take an electric signal about 40ns to travel from the center to one corner and back, and a signal certainly needs to do more than that in a clock cycle, so the physical limit on its operational frequency would be well below 25 kHz. If you want comparable computing power to a regular M1, you'd need to build a tower of them at least 100,000 high. On the plus side, you could build a city on the stack and no one would need heating in the winter. The cluster should be powerful enough to coordinate the traffic lights. Synergy!