Is the NR (or even the whole support for the 5DIII) better in DPP than in LR?
Quite possible. But likely it's ISO and scene dependent. Some software will handle it better than others (i.e. DPP vs. LR vs. DxO), and there are also dedicated plug-ins (Noise Ninja, Topaz Denoise). Fortunately, most offer some sort of free trial - you can test them all for yourself on the same set of images.Also, if I may ask, what was the subject that required exposing -2EV and then pushing it? That just seems like a recipe for noise...
Perhaps a black barbeque against the side of a white house? But in that case, pushing 2 stops wouldn't be nearly enough.
Serious subject matter requires serious equipment. C'mon Neuro, you of all people should know that. Now let's see your publications!