Using a browsermark-test (bit.ly/brmark) I found out the following: PR1.2 speeds up the browser about 17%. Results:

Before the update 600MHz: 8687 points
Before the update 800MHz: 11453 points

After the PR1.2 update 600MHz: 10141 points

I havent overclocked yet, someone could send the result for PR1.2 900MHz...

For comparison here are the average results...

iPhone 3GS: 26897 points

Nexus One: 23726 points

Droid: 14918 points

N900: 8646 points