Up until now, differentiating between CPU products has been all about getting more cores and higher speeds. If you have the money, for instance, you want to buy a CPU with as many cores as possible running at the highest speed possible in order to get the fastest performance possible. An article by J. Scott Gardener opened my eyes on how much more complicated a smart CPU buying decision will be in the future. In the past, CPUs were clocked as high as they could go (in terms of GHz ) and priced accordingly. These days, MANY (I will exaggerate a bit and say MOST) CPUs are actually capable of reaching incredible speeds far exceeding their marketed performance grades. For instance, it is possible to take a 1.8GHz Dual-Core Intel processor and overclock it to just about 4.0 GHz. In a simple sense, smart overclocking consumer x just doubled his performance for free. So why doesn't Intel, AMD, or VIA just sell consumer x the processor already set to 4.0GHz? Because smart overclocking consumer x had a serious heatsink or liquid nitrogen cooling his CPU. Most consumers don't opt for a mega-large CPU cooling tower or live in Siberia (ambient temperature has a measurable impact on CPUs).
At some point in the future, stating a CPU speed at retail becomes meaningless, because the majority of the produced CPUs can all perform far beyond the cooling capacity of normal cooling solutions. What becomes the differentiating factor at that point? More cores aren't always more useful if the CPU has to throttle itself to prevent overheating.
Personally, the only answer I can think of is some sort of thermal efficiency measurement. A higher value would mean the CPU could produce more performance for less power and less thermal output. The lower value CPU might produce similar performance, but require more power and a more vigorous cooling solution.
And, as always, this means that consumers get more for their money. Yay!