Silicon lottery, some chips are plain superior and run cooler. Dynamic clocks then come into play and allow the superior chip to stay boosted longer.
For GPU boost 2.0 if you set same clocks the max boost will be same on all cards. And it doesnt throttle down from the highest boost bin till after 75 iirc i did some experiments with it on air and water.
However for extreme ocs we disable boost so we can maintain the highest boost clocks at all times when loaded instead of a dynamic load
But anyway shadow was saying same clock on diff cards perform differently... I found that odd since same architecture and model work done per clock should be the same
Lottery only determines the voltage at which you can reach a clock and hence with locked chips, the highest clocks u can reach. But if all are kept stock regardless of good or bad chip would say its probably the same