The D3D gains are specific to 256MB boards. The changes that have been applied in the release have already been applied for boards with lower memory configs in prior releases (I'll let you o the research

), the threshold has just been moved up a notch to 256MB boards. It should only really be noticed in high memory utilisation scenarios, which means that there are fewer cases that will really stress a 256MB board - high res HDR and probably AA are going to be prime candidates.
The OpenGL changes should be a little more generic.