Why would you buy an expensive GPU when AE doesn't use the GPU? Unless you're using the obsolete ray-traced renderer, the GPU makes very little difference for AE (unless you're using certain third-party plugins like Element or Red Giant Universe).
nyway, here is more info on the GPU in AE: GPU (CUDA, OpenGL) features in After Effects
So, the GPU isn't the issue, let's find out what the issue actually is. What sort of things are in your composition? Tell us as much as possible and show us screenshots. Explain what you mean by "takes a lot of time to render". Give us the full specs of your machine. What are your memory and multiprocessing settings? What are your render settings? How much have you used AE in the past? Is this your first week with it?