The 2013 27-inch iMac with its fastest CPU should still be quicker though. I suspect if you had one of the 8-core models you'd see peak single threaded performance similar to what the 2012 27-inch iMac delivers.

Now part of this is exaggerated by the fact that I'm reviewing the 2.7GHz 12-core Mac Pro configuration. Granted everything else around the CPU cores is beefed up (there's more cache, many more PCIe lanes, etc.), but single threaded performance does suffer as a result. So while the latest iMac and MacBook Pro ship with Intel's latest Haswell cores, the Mac Pro uses what those machines had a year ago: Ivy Bridge. The Mac Pro follows Intel's workstation roadmap, which ends up being cut down versions of Intel's server silicon, which happens to be a generation behind what you can get on the desktop. If there's one graph that tells the story of why Intel's workstation roadmap is ridiculous, it's this one. I've already gone through Cinebench 11.5 results, but the following graphs should put in perspective the Mac Pro's performance relative to all consumer Macs:

Here we'll get an idea of how the new Mac Pro, in its most expensive configuration, fares as a normal Mac.

There are definitely multithreaded components to these tests (some are indeed highly threaded), but the suite also values good single threaded performance. For my final set of CPU performance charts I put the new Mac Pro through the same set of tests I do all new Macs.

2013 mac pro v 2017 mac pro