Would upgrading the video card imporve my export time?

I was searching the forum but most of the treads on this are outdated. I have a mac pro 8 core 2.26Ghz w/ 8gigs Ram and a NVIDIA GeForce GT 120(512 ram), I am wondering if I upgrade the video card if it will speed up my export times? I am still using FCP 6 and OSX 10.6.8 so I don't know if I am at a software limitation at this point or if upgrading would give me a performance boost. I was not sure where the beef of the rendering/exporting work comes from....CPU or GPU. Any info would be great. Thanks