I think your CPU that play 1080p H264 smoothly already by software decoder.
And higher score in game isn't equal to smoother H264 playback,example 8800GTX, old 8800GTS ...etc.(when you use low level CPU)
If you don't play 3D heavy game, you could buy ATI HD2000 serial VGA card.
Otherwise, you could buy ATI HD3870 or nVidia 8800GT/new GTS serial VGA card.