The August 2010 models offer 4/6/8/12 CPU cores at various clock speeds and widely varying list prices, ranging from $2499 to $5999 or more. There are far more choices than Apple has ever offered before, and this leads to some confusion about which model is best.
Since the CPU cannot be upgraded, understanding CPU clock speed and cores is critical for making an investment in a Mac Pro.
For example, the 12-core model at 2.4GHz will almost always be slower than the 6-core model at 3.33GHz (for most all uses).
Even the 2.93GHz 12-core model will often be slower than the 6-core 3.33GHz model. It all depends on your software and workflow. See the Shootout with the prior model— same idea. A new shootout is coming in August.
Paying more for lower performance won't feel good, so which model should you choose, now that Apple offers models with single or dual CPU, and 4/6/8/12 CPU cores?
For more discussion, see this page.