with a turbo the first number (cold) is important, as you want lubrication to the turbo as soon as it fires. 5w-30 or 5w-40 both work. don't get to hung up on the summer/winter thing, you've got an oil to water cooler that operates at the same temperature (192f) year round. the only real variable is the load the a/c puts on when it's used. as long as you're under warranty use what the manual tells you. their are many oil snobs and experts here, but in reality if it's good with vag, mb, bmw and porche, how bad can it be.