These are the books I've studied so far, all which I think are excellent and probably good to do in the order listed below:

1. Pandolfini's End Game Course  

2. Improve Your Endgame Play by Glen Flear   

3. Chess Endgame Training by Bernd Rosen

Would anyone have suggestions as to the next book you would read based on this progression?

Silman's new book seems like a good way to see where you are at, in terms of "a ____ rated player MUST know this" assessment.

Silman's book sounds good, and I would definitely get it if I hadn't already gone through my initial list.  However, I view it as a 1st (or maybe second) book on chess endings.  At this point, I don't think it add's anything other than what you mention ('know where you are at concept'), which is ok but I wouldn't buy the book just for that.

"Essential Chess Endings" by James Howell, if you can find it.  Read Silman's review of it.  Simply the best one-volume readable book yet written.

I agree it's a very good book, but very hard to get at a reasonable price!

Also, I think it targets more towards the beginning (1st book on endings), although I could be wrong.

I believe it is aimed at the intermediate level.  At the beginning level Averback's "Chess Endings-Essential Knowledge" or Znosko-Borovsky"s "How To Play Chess Endings" are the best.

BTW--Rosen's book is great.

I agree 'Chess Strategy in Action' would be good (middle game), but I don't think I'm ready for it.

I couldn't quite get through Pachman's 'Modern Chess Strategy' in my first try.     But hope to give it another go later in the year.