[vafan13]

40 weight ended up being added as an optional oil choice for our cars sometime after they were originally released, so there's nothing wrong with using either. In general folks feel safer with 40 weight and some, like me, have seen reduced oil consumption. I imagine the tuned guys are even more likely to run 40, but it certainly isn't limited to them.

Whether 0w40 or 5w40 would be better is dictated largely by which oil one uses. For some, like Mobil 1 and Castrol Edge, the 0w40s have historically been higher quality oils than their 5w40 counterparts. Another thing to note with 0w40s is they are on the lighter end of 40 weight, so less drastic of a jump from a 5w30.