it depends. if the video card is only using 256mb of its 256mb then it will only effect the performance of the physics in the game. if its using over 256mb of graphics memory, then it might have to backup the memory in the system memory... ultimately takinga larger toll because the data needs to travel from the memory to the cpu to the video card.
either way the 3.4GHz proc will make the game perform better, because the physics will need to be processed either way.