Sade would not have published anything in 1758; he was I think about 18 years old at the time. Voltaire's <i>Candide</i> was indeed irreverent but not "scandalous" in the way Sade would become. As you point out, Voltaire was very well respected among well-educated French and Europeans; he had been closely associated with the Enlightenment (especially its criticism of the clergy) but not thought of as immoral or decadent, as Sade was.

In any event, Voltaire's reputation benefitted from being away from Paris from the early 1750s until the end of his life -- it helped him avoid getting caught up in the increasingly tense domestic politics of the time.

A more controversial work, in the 1760s, was his <i>Dictionnaire philosophique</i>.

Finally, indeed, Voltaire did write very critically of Rousseau, especially following the publication of his <i>Letter to M. D'Alembert on the Theater</i> in 1758; Rousseau's critique of high culture as socially decadent drew Voltaire's ire. However, as you no doubt know, <i>Candidate</i> was really much more a critique of Leibniz.

A very good, readable discussion of <i>Candide</i> in 18th-century context is Daniel Gordon's introduction to his translation of the novella, published by Bedford Books in a cheap paperback.