Thats not true. It was when that video was posted all over the internet, but AMD has had power stepping technology for a while now. FWIW I had a room mate a while ago. I was helping him solve a windows issue, he had a P4. It looked like it was overheating. Well he had the HSF off, and that baby cracked before it even finished posting. Not like in that video where it started to smoke a little..... smoke and crack. So, just realize where the propoganda is coming from on that one.
From what I hear also, the X2 6000 actually comes close in performance to the C2D 6400. But for me, I had an X2 4400, but not AM2. So I needed to get a new MoBo anyways. At that time, about 3 mo ago, it was clear to get a C2D.
And as for clock speed, yeah. Look at the NV 8xxx vs ATi 2xxx. ATi is much faster.
All in all though, these C2D perform very well and were actually very well priced from previous generations.