Historically Adobe software works best with Nvidia cards and Apple software works best with AMD cards. This is partly down to Adobe software being designed to benefit from CUDA as provided only on Nvidia cards.
For Nvidia cards Nvidia provide drivers themselves and you have to use their drivers to also use CUDA. Apple are the only source for Mac AMD drivers but also provide Nvidia drivers but not CUDA drivers. Sadly Apple have a history of producing mediocre at best drivers. I see they are currently advertising for video card driver engineers but I do not expect this to result in a sudden improvement.
There are two main competing GPU processing standards CUDA as mentioned which is only for Nvidia cards and OpenCL which is in theory usable on both but historically has been better on AMD cards and in anywise is not what Adobe aim for. However Apple did recently port their 'Metal' standard from iOS to Macs and this works on AMD, Nvidia and even some Intel GPU chips. Metal does appear to deliver massive performance improvements.
Unfortunately even though initially an Adobe representative not only demonstrated using After Effects modified to use Metal, see https://www.youtube.com/watch?v=Zp1aPgLx4RQ Adobe since then have completely backtracked on the idea of using Metal even though it clearly delivers massive improvements and they themselves have shown it is practical to use.
Many Mac users are livid over this. See http://www.macrumors.com/2015/10/05/adobe-backpedals-metal-after-effects/
So right now it can potentially be possible to upgrade an old classic Mac Pro with a new Nvidia card or cards and make a much more powerful system for running Adobe software.