The speed increase is highly overated. A few items that make use of the new "Mercury Engine" GPU are faster. The Liquify filter is most often given as an example. For basic work, I see little or no difference over CS5 on the same machine. Add some normal adjustment layers, tweak some sliders, do some masking, flatten... all the same speed as before.
And ACR raw conversion is significantly slower because of the new "Process 2012". But you get what you pay for. The new ACR process 2012 is a major improvement.
Take a raw file and adjust all sliders, especially noise removal and CA removal. Convert it in both CS5/Process 2010 and CS6/Process 2012 and see the difference. On my Windows 7/I5 system CS6 ACR takes 50% longer to convert. The noise and CA removal and the major culprits.
