: denotes magnitude or intensity
: despite; denotes a contrast
Ex: I will not give it to you even if
you are giving me the moon
should be right because you are talking about intensity. Even if you get me the moon, I will not give you what you are looking for.
Ex: Although you are a nice person, I will not give it to you.
Although is right here because it means despite the fact that you are nice, you will not get it. There is no intensity involved here as in the first example. The contrast is established as follows: In normal circumstances, a nice person would get it. In this case, although you are nice, you will not get it. There goes the contrast.