Comment by kickopotomus

We stopped chasing clock speeds because of the physical timing limitations of gate and signal propagation. Not because of heat. Suppose you are using a 5GHz clock. Every cycle is 0.2ns. Light can only travel 6cm in that time. Electricity propagates a little slower through a conductor (and even slower through silicon). So if you are using some insanely fast clock, you are just wasting cycles waiting for signals to move across the chip.