If I understand this correctly, it should be possible to use a font which does not need to be antialiased again and use (dabbler googling) wxGraphicsContext::SetAntialiasMode() with wxANTIALIAS_NONE. Then it could be nearly the same result as the previous stamp without losing portability?
If yes, then this is a vote for doing it like this. If not - well, then at least the size could maybe slightly increased?
Thanks and
Good Luck