Why is my Mac's CPU throttled? (Turbo Boost Ratio)
So, I ran some Cinebench R11.5 benchmarks to get more information about the single threaded performance of my i5-3427U1 (1.8-2.8 GHz) CPU:


  1 thread &#x2192; 1.10


I also contacted the author of the linked article by AnandTech - @anandshimpi2.  Anand Lal Shimpi was so kind to send me a benchark chart which compared the single threaded performance of the 2011 13" Macbook Airs with the 2012 13" Macbook Airs using Cinebench R11.5.

Into this picture, I have added information about the maximum single threaded CPU clocks along with a comparison of the measured performance such as Anand Lal Shimpi has suggested.


[image source]

In this info graphic I am comparing specifically:


  
  2011 13" Macbook Air, i5-2557M 1.7GHz/2.4GHz/2.7GHz
  2012 13" Macbook Air, i5-3427U 1.8GHz/2.6GHz/2.8GHz
  


As you can see, the single threaded clock of the 2012 model is 3.7% increased in turbo boost mode.

However, the benchmark score saw a 9.9% increase which is not simply due to the higher clock, but also due to the more efficient Ivy Bridge architecture which is about 5-15% faster3 than Sandy Bridge. 

In sum, the benchmark scores are as expected whereas the Turbo Ratios log entries are not. Anand Lal Shimpi had "figured it was a bug, submitted it to Apple back in July"4.