Bare Feats has run the tests, and the 2012 iMac 27″ 3.4GHz Core iMac with 32GB of RAM and the GeForce GTX 680MX GPU actually does beat the MacPro in Resolve and Premiere Pro, but that is a MacPro with the Radeon HD 5870 GPU. Not really a fair test unless you have an NVIDIA CUDA card in the MacPro. As the MacPro still beats the iMac in 2 out of 3 CPU tests.
I have a feeling my non Mobile NVIDIA GeForce GTX 670 4096 MB would slaughter the iMac in anything CUDA aware, which would be Premiere Pro, After Effects or DaVinci Resolve.