We asked NVIDIA about the changes in the new VDPAU feature set and what it meant for Windows users. They indicated that the new VPU was a faster version, also capable of decoding 4K x 2K videos. This means that the existing dual stream acceleration for 1080p videos has now been bumped up to quad stream acceleration.
Feature Set D hardware decoder is very impressive. It's very fast, 120FPS 1080P H.264 decoding, easily outpacing Feature Set C decoder.