You'll find below a screenshot from a Word 2010 document, where I typed two 'b's, both with the 26 pt Cambria Math font (both characters have bold). The character on the left was typed using the text editor. The one on the right was obtained inside the Equation Editor.
I believe the first glyph is 0x0A86 and the second is the glyph 0x0888, but I can't understand the criteria for these options. I would also appreciate if somebody could confirm whether the glyphs mentioned above are correct.