I have an older MacPro (2010) Quad core, 2.8 Ghz, 16 GB RAM with an ATI Radeon HD 5770 graphics card. I am trying to get the most out of this machine before buying a new one (hopefully not before the end of the year). I use After Effects CC daily for motion graphics (very little 3-D stuff)...would like to get advice... Will an upgrade in graphics card to Sapphire HD 7950 show improved performance? How about GeForce GTX 680?
Unless you are using the Ray-Traced 3d renderer, getting a different graphics card won't help with stock AE. If you use Element 3d or some other 3rd party plugin that relies on the GPU, you might see a difference, but it depends on the plugin.
The GPU is used very little by After Effects. See this page for details:
Spend your money on SSDs, RAM, and a better CPU before you consider spending money on a new GPU.