I don't think that this is true. I do have afterburner/rivatuners on screen display and I do only have 1GB of vram. At my current settings, its set to use 1.1GB with everything high/very high except for post fx and textures and population variety turned down. I experience no stuttering and my vram usage remains below 950mb. Now when I turn textures (textures have a very low performance impact other than needing the vram) to high and vram enters the 1800mb range, stuttering eventually occurs although the vram usage isn't marked as high.