As for edge retention, the other steels that you mentioned are certainly better than 440C. But my experience is that they are not that much beter. But some of the exotics are certainly a bit better at attracting rust. Look at ZDP-189. As mossyoak pointed out, Sal has to sandwich this exotic in between 440C because it'll rust so easily.
But as far as D2 goes, oh yeah it's got extremely good edge retention over 440C, and practically over everything else out there too.... And you need the patience of a Saint in order to sharpen a dull D2 blade. That, or access to some laser-sharpening equipment.
ZDP-189 doesn't have to be laminated, but laminated is cheaper and easier to work with. Some Spydercos have solid ZDP blades; CF Stretch, ZDP Endura and Delica.
I EDC a ZDP Stretch and there is no rusting and it stays sharp for ages. A bit of a ***** to sharpen though.
D2 is easy compared to ZDP:nana:
For most users all the higher end steels will perform very well. If one is inexperienced with sharpening and don't have a good sharpening kit some of the higher end steels are a nightmare to sharpen.
There are several reasons to use carbon steel in outdoor fixed blades; cheaper, better toughness, smaller carbides and tradition.
I like A2 in my fixed blades, but 52-100 and several other carbon steels are very good. AFAIK there aren't any stainless steels out there that will beat good carbon steel in performance. The only advantage they have is ease of maintenance
That said I like stainless in my folders since they are harder to clean.
Sverre
