Did you watch the video? The 920 outperforms the 620 in every discipline except two: boot time and WiFi handshake.
Ignoring that the test couldn't be any less scientific, it does at least show how little impact a higher CPU clock rate has when using normal apps. The 620 is clocked at 1GHz, while the 920 is clocked 50% higher at 1.5GHz, yet the performance difference is often barely noticeable. The performance difference is most noticeable in 3rd party apps which execute within the .NET runtime. Those apps are obviously somewhat "heavier" than the 1st party native apps. For the later, the performance difference due to the higher clock rate is practically non existent.
Also, the only perceivable difference is in application load times. Once the app is loaded there doesn't seem to be any difference between the two.