With no first hand experience in graphics design, from my experience with engineering CAD, animation, and video editing software, I'd say that the 480 and 970 are probably tied. In my experience, especially for the older versions of software you find in a lot of corporate or education settings, CUDA is way better optimized than OpenCL. However, the RX 480 isn't a weak card and a larger frame buffer helps a lot too. I don't think you can decide w/o seeing benchmarks on a similar workload. Doesn't AutoCAD Maya have a benchmark suite?
Ideally, I'd want something like one of the new Pascal Quadros coming out, but who's got that kind of cash? Quadros will have the same overall performance as the geforce counterparts, but have some extra features, e.g. 10 bit color, etc enabled in their drivers and more stable drivers overall. For most amateur/prosumer scenarios, it doesn't matter.
Really, the same general ideas as choosing a GPU for games apply. Pick the one with the best benchmarks that you can afford. I'd wager that right now, those charts are topped by GTX 1080/Titan X SLI setups.
Edit: Here's the Blender (animation software) benchmark results for a whole variety of setups. My assumption is that the workload is not dissimilar from what you're trying to do.
http://blenchmark.com/benchmarks-overview