What is the best compression level anyone was able to get on either Monster and City of God using Shrink?

i don't understand the point of this question. the answer would obviously depend on how much you leave out, with the "best" coming from only leaving in the main movie.

Yup, movie only will always produce the best results, leaving you with little or no compression. If I am going to keep the menu and special features then generally what I do is set the compression on the menu and special features at maximum and devote as much space and quality as possible to the movie itself. I mean really, how often are you actually going to watch the special features or sit there and stare at the menu. It's still watchable and quite functional but the movie is really where you want your quality to be.