.... and there are 4 of them on a motherboard.
Why 4? Not 8?
There's an end somwhere. In real world it will be power or price before performance. Why? Performance scales lineary, power and price does not...
As I said, ratios counts most. If you hit power limits in performane/power ratio then you can do nothing. If you change that ratio to 6/2 then you can increase performane 3 times...
That is the point, you do hit a limit in performance/power ratio, it's Voltage squared, so
1V^ =1 and 0.5V^=0.25, 1/0.25=4/1=8/2 minus static power, minus supporting electronics = 6/2 to 4/2
1V^ =1 and 0.6V^=0.36, 1/0.36=~3/1=6/2 minus static power, minus supporting electronics = 4/2 to 3/2