Broadly speaking, your GPU doesn't affect final renders unless you are actually using the Maya Hardware Renderer to create your final image. After all, there may be cases where you want to send your render to an entire farm of machines that don't even have video cards at all.
That being said, I am kind of old and out of touch with the latest developments. It's not impossible that there's been some work done to integrate GPU calculations into mental ray renders... I just haven't heard about it myself.