And if I understand it correctly, lowering core voltage forces the GPU to perform 'more work per watt' while setting power limit simply sets a hard limit on power consumption, forcing the GPU to throttle down rather than suck more power when it approaches the set limit. Right?
1) Correct. It does the same work while using less power and producing less heat. But at some point it will get unstable.
2) Correct. Less work but also less power and less heat + safe & stable.