Well of course GHz means SOMETHING.. .. It's one of the two main components of the efficiency formula..
Instructions/second = instructions/cycle x cycles/second
The cycles/second = GHz measure
AMD tends to have a higher "instructions/cycle" than Intel. It just so turns out that when u combine the two components, to get the same "Instructions/second", you only need a lower "cycles/second" for AMD..
But yeah. Both the "instructions/cycle" and the "GHz measure" are obviously important.