Ae primarily uses the CPU for rendering. Ae benefits most from many fast CPU cores and lots of RAM.
The GPU is used to accelerate renders only for the ray-tracing renderer introduced in CS6. You must have an appropriate NVIDIA card with CUDA for this acceleration; otherwise it will fall back and render on the CPU.
Some effects may render on the GPU, like Element 3D or Magic Bullet Looks. Most of these use OpenGL, so a single mid-range GPU is usually sufficient.
If you have some very specific render requirements, let's talk about what you're doing.
Walter Soyka
Principal & Designer at
Keen Live
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
RenderBreak Blog - What I'm thinking when my workstation's thinking
Creative Cow Forum Host: Live & Stage Events