Cambria Math uses Microsoft OpenType math extensions.
Word 2007 and later understand them and display text at reasonable intervals.
However, Notepad and Word 2000 display text at huge intervals, like winforms. I assume the font has such a default space because some characters (e.g. U + 2320, upper half of the integral) are much larger than alphanumeric characters.
If you use Cambria Math with a font engine (such as the one used by winforms) that does not understand math extensions, you will get a large spacing.
If you show simple expressions, you can also use Cambria.
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