Porsche has released a video in which it talks about the new 7 speed manual transmission and the optional PDK gearbox in the 2012 911 (991).
As it describes the way the 7 speed manual works, the automaker from Stuttgart says that gears 1 to 6 have a sport ratio and that the top speed is reached in 6th gear, while the 7th gear has a long ratio and it ensure low engine speeds even when travelling at high speed for long distances. As you can imagine this 7th gear helps reduce fuel consumption.  
As for the optional PDK dual clutch gearbox, Porsche says it also has 7 gears, and that apart from concentrating on offering relatively low fuel consumption figures, it also guarantees the best acceleration with no interruptions.
 
 
 
 
 
 
 
 
Video: 2012 Porsche 911 7 speed manual transmission

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Source: Porsche via YouTube