I would think that they are talking about clock frequency. They do say that you can either have the 37% performance increase, or use less than half the power when at the same performance.
It's probably easier to use that much less power for the same performance than to push the same power in and get higher performance. On smaller size scales power leakage and heat dissipation become bigger issues so you might not be able to push the same amount of energy through as with the larger scale chip.
