|The new iMac, notice the Blackmagic Cinema Camera :-)|
The new cards are based on Nvidias mobile GPU chips, the same ones that are used in laptops, the 21" iMac can be configured with the GT640M or GT650M (as found in the retina display MacBook). The 27" iMac can be configured with the GTX 660M, the GTX 675MX or the GTX 680MX.
The GTX 680MX has 2GB of RAM and 1536 CUDA cores, making it an excellent choice for CUDA accelerated software such as Adobe Premiere and After Effects.
DaVinci Resolve should run well on these new iMacs, although with some of the same restrictions as the Retina display MacBook. There doesn't seem to be any way to use the Intel graphics in the processor for the UI whilst using the Nvidia GPU for processing.
One thing to take note of is that Apple are now using Nvidia chips in all their latest systems, moving away from AMD, so those of us who are running PC versions of Nvidia cards in our Mac Pros needn't worry about support being removed from OSX :-)
What do you think? Let me know in the comments.