Doesn't the i7 920 have 8 cores?
No, although Octo-core microprocessors exist.
A version of the i7-Extreme has 6 cores, with a p.v.r of about 20.2.
The Phenom II x6 hits a p.v.r of about 19.8.
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For a comparison, an Xbox 360 is 9.6, an entry level quad core is 9.2-12.6, and a high powered dual-core can get up to about 7.
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They are pretty evenly matched, but Intel takes the cake by a small margin with their processor. I agree with radial about how companies need to just come up with more efficient technology already, rather than stacking.
Based on benchmarks from a source I can't remember, you will hardly be able to tell the speed difference between the two, but apparently Intel's is a wee bit faster.
I want one... My Quad-Core Phenom is starting to bore me. :P
P.S: Expect an octo-core i9 about 216 days after the release of the new iPhone.