Many tasks would be faster with the higher 3.9GHz turbo clock speed of the 3.0GHz 8-core Xeon E5 1680 v2.
If you read my 2010 Mac Pro review, you saw that applications, even professional ones that cost thousands of dollars, rarely use more than one core for many operations. Finding the best performer this time around is less straightforward and depends on your task. In the past, you could spend more and get a faster chip with the same total core count.
If you do decide to do a CPU swap yourself, keep the old CPU around in case you need support. Teardown and tests by OWC revealed that the CPU is user-replaceable, but that may not be much incentive to upgrade for a $700 savings over Apple's 12-core price. Apple pays less for this, but you get the idea-this is the priciest generation of Xeons I've seen from Intel. The 8-core E5 v2 retail price is around $1800, and the 12-core is a crazy $2750 at Newegg. The price was a big one-it's never been this expensive to get a mid- to high-end Mac Pro, largely because of how expensive this round of Xeons are. I've never seen a generation of CPUs complicated so much by a variety of factors. It was not an easy choice to buy the 8-core over the 12-core, especially since I do 3D work most of the time. At this point, you're probably disappointed that I didn't buy the 12-core machine because you wanted to see it stomp all over everything.
