The rendering is done completely by the blender internal raytracer, your video card is not involved in any way. more ram doesn’t help all that much either unless you are rendering projects that take a lot of ram. so long as you have more ram in your computer than blender needs, you should be fine. The big thing is streight up processing power. Since blender currently only handles two threads, the core2 extreme will not be any better than a core2.