To reinforce what Chris has said, keep in mind there's only one processor package in the new Mac Pro. There are cases where having two packages - such as in the previous design Mac Pro with dual Xeon x5600 series processors - can actually be a pretty big advantage.
That being said, I've put a lot of thought into how many cores a new Mac Pro ought to be configured with to run graphics software well, and I've come to the thought that 4 is too few and 12 is way too many. I believe the 3.5 GHz 6 core E5-1650v2 may actually have a slight edge over the 8 core E5-2667v2, because with 12 logical Ivy Bridge processors cranking full-on (with Hyperthreading) the memory bandwidth is actually already going to be taxed. And of course the 6 core is much cheaper.
There's a nice little Photoshop benchmark that's reasonably indicative of how well a system actually multithreads with Photoshop. It can be found here:
I have a PC workstation with the same chipset as the pre-cylinder Mac Pro (dual Xeon x5690s in my case), and my best speed for that benchmark with Photoshop CC equals the best posted on that site: 8.3 seconds. People are reporting the new Mac Pro is scoring with that benchmark in the same vicinity - but not really faster.
Do some research yourself and see what various folks with the new cylindrical Mac Pro are scoring on that benchmark. I'd be interested to hear if your findings are like mine.
What's your system score, Chris?
-Noel