Well, the Academie doesn't have as much power as it thinks it has, but its power is considerable nonetheless: it can force the government, the press, teachers, TV and radio, and all official publications to write/speak as it says. In the long run, this won't stop popular usage, but it does tend to slow down change--when I lived in Paris, slang from 50 years earlier was still current. I don't say that the Academie caused that state of affairs, but it certainly influenced it, IMHO.
I'd think that Voltaire's French is more or less Camus'--at least, I don't remember any substantive difference, even down to the literary past tense. But by the time you get back to Corneille, I think there would be differences, at least spoken ones. I know the final y-to-i change dates after this, and there's a pronunciation shift that accompanies it. I'm sure there are others; after all, this is when the Academie was first constituted & began pruning the vocabulary of 40-50,000 words or so.
And when you get to Rabelais, the transformation is complete. It's hard to read him as modern French, harder perhaps, than Shakespeare as modern English.
YHOS,
Snarkhunter