What Unicode Font is Best Suited for Math Symbols using Font-Locking under Emacs?

As suggested by egreg, I will turn my comments into an answer to at least part of your question:

One would think that perhaps the Computer Modern fonts themselves might exist in some form (encoding + format) that would allow them to be used from within Emacs, and if so has anyone had success using them for this purpose?

You could use the CM-Unicode fonts, which are installable under Windows on OS level and therefore usable from all applications using the system fonts. I use these fonts in Inkscape, Word and PowerPoint.

Quoting from the CM-Unicode homepage:

Computer Modern Unicode fonts were converted from metafont sources using mftrace with autotrace backend and fontforge (former pfaedit). Their main purpose is to create free good quality fonts for use in X applications supporting many languages. Currently the fonts contain glyphs from Latin1 (Metafont ec, tc, vnr), Cyrillic (lh) and Greek (cbgreek when available) code sets and IPA extensions (from tipa).

You also ask about STIX fonts. These fonts are also available in otf format, so I would say it should be easy to install these fonts on system level.