As far as Cheetah is concerned (and the majority of other 3d apps) the CPU is the thing to pay attention to the most, as it is what the renderer uses.
For Cheetah yes, the rest not anymore. Most renderers use the gpu, too, and sad as it is, nvidia-cards for that. And it's faster than CPU-rendering. Even the native modo renderer which is still CPU-only has in the new version an inbuilt denoiser that works only with nvidia (nvidia optix. You find it in the final color output properties). And they will get ProRender (it's still in testing).
ProRender is from AMD and of course for their cards but works with nvidia, too. But it still isn't finished and while it gets some stuff beautifully rendered, there is still a lot missing. Martin somewhere stated that it could be integrated in Cheetah one day.
So a dedicated GPU, even just a decent one like the one I expect they will use in the coming iMacs, will be a lot more useful in the near future. But as Mis said: It's important to wait for the next batch of iMacs. And of course it's the question what kind of processors they'll get.
The actual 8 core i7 doesn't have multithreading, only the 4 core and the 2 core i7. Which ... well ... somehow astonished me. A 2 core i7? That doesn't mean it can't be faster than (some) older ones with 8 threads. But it will be necessary to look into it.
That said, and I know i'm a minority of one, I do prefer cpu- over gpu-rendering because of the cost (at least there are external graphic cards around, so if it gets to be a problem, it can at least be solved. But it's expensive, too).
The new iMacs will hopefully still have the possibility to upgrade RAM later on (it's even easy with the older ones).
The other point are the monitors. As Swizl stated, those things are quiet expensive, it's not sure how smoothly a similar resolution runs on a mini, and the iMac has just a beautiful picture.The color space is not the adobe one, of course, but something apple specific (I like it). And Full HD really is just pixel-pulp compared to a 5k-monitor (but at least with my right eye, i still see the grid).
So i would go for the iMac, at least as long as it's not known that Apple somehow messed them up, too. For professionals or dedicated hobbyists, they want to sell the iMac Pros ...