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Upgrading the Mac Pro CPU
You can upgrade the CPU to a faster clock speed, or dual CPUs instead of a single CPU (2009 and 2010 Mac Pro only).
In general, a fast clock speed is best for most users, but whether 12 cores is better than 4/6 cores depends very much on the specific tasks involved.
Upgrading the CPU is relatively expensive; you’re better off buying a faster Mac up-front, because Apple can offer the fastest CPUs more cost effectively than is possible through any upgrade service (Apple gets a very large discount on some very expensive Intel CPUs).
Consider cores carefully
Assuming that 12 cores are better than 6 cores can sting: once when you pay extra for the “faster” system, and then in diminished performance for as long as you own the machine.
By the same token, 12 CPU cores can offer a major benefit for some programs.
It all depends. And the facts could change when system software changes, or the application is upgraded (usually for the better).
With Photoshop CS5, 12 CPU cores kills performance compared to 6 cores.
Adobe is working on this issue, but no solution had emerged as of February 2011.
With Apple XCode, 12 cores is a Good Thing.
XCode pegs-out all CPU cores. Developers will love a 12-core system.