Under OS X, this is still a CPU test - the GPUs remain idle and out of the picture here.
I received a reader request to try running the Cycles benchmark in Blender (an open source 3D renderer), so I'll start with that: I grabbed the 2012 15-inch rMBP, the entry level and upgraded 2013 15-inch rMBPs as well as the new 27-inch Haswell iMac for comparison.
With the legacy Mac Pro comparison out of the way, I wanted to put the Mac Pro's performance in perspective relative to other high-end, modern Macs. Putting Mac Pro Performance in Perspective: Professional Apps
