The most appealing would-be explanation of the difference appears in one of the comments made in response to the posting under your third link:
Suasion is the deployment of rhetorical means for the sake of moving the audience to the rhetor's position. Persuasion is the effect or result of successful suasion on that audience. One can thus suade an audience yet fail to persuade.
(Though note that here the verb 'suade' seems to have been included as a nonce word, as it is otherwise obsolete; Noah Webster said so as far back as 1828.)
All this being said, I haven't found any evidence for the distinction made above in any of the dictionaries I have so far consulted, which all essentially describe both suasion and persuasion as "the act of influencing or persuading".