Re: Key-binding clash between gnus and calc

[Richard M. Stallman]

    C-c C-SPC

That's fine; it's reserved for major modes.

    C-c `

In the Lisp manual it says

    @item
    Sequences consisting of @kbd{C-c} followed by any other punctuation
    character are allocated for minor modes.  Using them in a major mode is
    not absolutely prohibited, but if you do that, the major mode binding
    may be shadowed from time to time by minor modes.

So you might want to change ` to a different character.