I've been using M1 HM 5w30/YZZD3 in my wife's 4th gen--but I've been thinking of moving to a 0w30 or 0w40 for hers and my 3rd gen.
With a Charleston, SC location, what do you expect to gain from an 0W-## ? Unless you're spending time close to Canada in the winter, you're really only concerned about the "30" part of the spec. Considering Toyota back spec'd most of us to 20 weight at some point, the only thing that's likely to happen if you go to a -40 is less mpg. FWIW, I've stuck to the 5W-30 spec despite the 5W-20/0W-20 updated spec.
-Brent