What is the best graphics card for After Effects CC?

Hi,

We are looking at new graphics cards for our studio, and want to know:

a.  What is the best NVIDIA graphics card for After Effects CC?
b.  What is the best AMD graphics card for After Effects CC?
c.  How many GPUs can After Effects CC utilize for processing?

Lastly, do you have performance benchmarks for the program with these GPUs?  Thanks for your help.

Rhea