Cambria Math uses Microsoft's mathematical OpenType extensions.
Word 2007 and later understand these and display the text with reasonable spacing.
However, notepad and Word 2000 display the text with enormous spacing, just like winforms. I guess the font has this much space by default because some characters (like U+2320, top half integral) are much larger than the alphanumerics.
If you use Cambria Math with a font engine (such as the one used by winforms) that doesn't understand the math extensions, you're going to get the big spacing.
If you're displaying simple expressions you might as well use Cambria.
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