The German 0w30 Syntec is in a league completely ahead of the US made 5w30 and 10w30 Syntec. It is simply a much more advanced oil, that passes much more stringent European specifications that the 5w30 and 10w30 can't pass.
And since the 0w30 is on the thick end of the 30wt range, and the other two viscosities are on the very low end, the 0w30 is actually a much better choice for the summer! And the 0w30 actually holds it's viscosity better than their 5w30 and 10w30. I've seen UOAs where 10w30 Syntec has thinned out to a 20wt, something that I feel just should not happen with a 10w30 synthetic, even if it uses a group 3 base oil.