In my opinion D2. it is very close to the level of chromium that makes a steel "stainless" ~13% according to the steel chart provided online by spyderco knives. All the knives I make are D2 and I have never had an issue with them rusting. You could always put a light coat of some various type of rust preventer on the blade for long term storage, I use Boeshield T9.
Again, just my $.02
Post pics of the blade when done.
TBRA