Comparing performance between the 2012/2013 MBA 13' baseline model
Have a look at the CPU die micrographs and reviews in the press and all are singing the same tune:


modest CPU performance gains
significant overall power reductions
dramatically better GPU - competes with mid-range dedicated GPU where the 4000 level graphics were adequate at best and lagged behind it's era of mid-range GPU substantially in many cases.


I would say the 2013 Air are a significant step up from the 2010/2012 models - enough so that I'll be selling and upgrading as soon as I can find a buyer for my current Air.

Although you mentioned only the CPU and GPU, the flash storage is benchmarked at 45% faster than 2012 (and now 9x as fast as 5400 RPM drives) and they have the 802.11ac wireless chipsets so it's quite the improvement overall.

The reviews are coming in and they seem to confirm my thoughts that the "slower" CPU in the 2013 models get more work done than the "faster" CPU from the 2012 models. Clearly the clock rate isn't the bottleneck for these tests.



The full article is the source of this image above: http://www.macworld.com/article/2041698/review-latest-intel-chip-boosts-speed-and-endurance-in-new-macbook-air.html