When you max out a Savage Species monster advancement you should be EXACTLY like a Monster Manual monster..same base saves, BAB, number of feats, special abilities, bonuses to abilities, etc. I know what Savage Species is, I will have an Astral Deva playing soon and there are glaring errors. If you don't believe me, that is fine..but why does it have electricity resistance AND immunity? I rest my case. Do what you will, but there are a few errors in the Astral Deva(Lack of DEX bonus, becoming large size, the resistance/immunity problems).
Also, the Monster Maual does tell you how to decompose a monster into it's base pluses to stats. I just don't remember where, it's in the back though.
Gariig