Penryn is a die shrink across the board. All server / desktop / notebook revisions will be available. It will not cost over $1000 (what Desktop processor does?)
A program that is multi-threaded is multi-threaded. They don't code dual core program, or quad core programs. They code multi-core programs. That means the processor could be 256 core and it would still be utilized by the multi-core program.
And yes, generally twice the cores will result in twice the performance of a multi-threaded application.
I am not sure what game we are playing?
Penryn is not just a simple die shrink:
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From anandtech blog on Penryn.
Again, from what I understand, AMD was demo'ing the performance per watt. As you'll see here in the link, Intel's own dual cores and quad cores beat out it's own v8 system in a lot of benchmarks.
Your idea that multithreaded=fully utilizing all the cores, and that 2x the cores=2x the performance is severely flawed.