Original north american oil spec should have been 5W-20, BUT, the history behind that is that they only changed from 5W-30 to 5W-20, to raise fuel economy averages, well that and modern 5W-20 semi-synthetic is better quality than yesteryear's 5W-30 dino oil.
However, the same is still true today and more so. A high quality full synthetic 5W-30 will give you better engine protection than same quality syn. 5W-20, but slightly worse fuel economy. I'd take the protection over the minor fuel economy difference, though if I were north of the border, in Canada, then I'd go with a synthetic 0W-20.