Their information is on the web page www.armyoforr.com.
The main differences are looks, one has a rail mount for sights (NK), low pressure regulator, weight, inline regulator, and i think orracle operates at a lower pressure.
Oh, another important point:
The Nightkast has that god-awful half dust/half gloss anno. I don't know what they were thinking when they dreamt that one up.
If I were buying a WGP cocker new I'd go with the SuperStock. It really isn't missing much of what the NightKast has (main things are the externally adjustable inline reg and lpr), and for the $200 price difference you can easily swap out the crappy parts. Not to mention I think the 2K3 stock bodies are nicer looking than the Outkast and aren't annoed by some drug addict.