The 80% rule gets misapplied from time to time. For branch circuits the wiring has to be 125% of the load ampacity and the CB trip setting is for 125% of the continuous load in order to allow for in rush and prevent nuisance tripping.
The 80% rule is a UL rule that prevents you from overheating the wiring downstream of the CB and typically applies to conductors larger than #10. This is because the NEC states the exact protection for wire sizes #10 and below. The NEC specifies a 30 amp overcurrent protection device for #10 wire because of it’s use in residential applications. 2500/220 = 11.4 amps per miner, so two is the max for this circuit with a 30 amp CB.
I went into that detail because you would not necessarily have to add another circuit. If your PDU was rated higher and you used #8 (or larger) wire you could just increase the size of the breaker. This is something to run past your electrician and could save money compared to pulling a new circuit. Above a #10 you would use a larger breaker that would trip at 125% of the continuous load and wire sized at 125% of your continuous load.
Miners would be a continuous load because they run for more than 3 hours at a time. If you had cooling fan or electrically operated damper (let’s say 5 amps) for heat control that ran intermittently you would only size your conductor for 1.25*(miner total current @11.4 amps per miner) + 5. The NEC says 125% of continuous + 100% of noncontinuous load.