I use the following methods to rasterize font characters into a texture and then render them as a mesh :
It works great. I want to know font line height (the space between two lines).
In my case I only know the font size at runtime (which I specify as a parameter in RequestCharacterInTexture() and GetCharacterInfo() methods).
Ideally, font class would have a method as such : GetLineHeight(int size).
I also took a look at CharacterInfo structure, which give some information about how to render a character (for a given size) but it does not have what I want (line height).