Jay had it right. People freak over the "0" part, they just think it is too thin. I asked a guy at my local AutoZone if they were going to be getting any more of the 0W30 Castrol {didn't elaborate on the German/American versions as I figured he wouldn't know}. His reply was- {It don't sell too well, stuff is too thin. I tried some and the pump wouldn't pick it up. Too thin.} I didn't even argue, wasn't worth it.
I have used M1 0W30 in my 2000 Firebird since it's 3rd oil change at 6K miles. The engine now has 36K on it now. It's oil consumption is very low, the most it ever used was about a quart in 7500 miles.
I did alot of playing on that interval {quite a few 1/4 mile passes, around 20 or so AutoX runs and a lot of playtime in the mountains. I'm not easy on the car at all!
That's about the worst oil consumption interval it's had. Most of the time it uses around a 1/2 quart in around 7000 miles. Don't know if I'm lucky or not, most tend to say the LS1 is a oil burner.
If I rember right, the 0W30 is a bit thicker than the 5W30 or the 10W30 M1s. That might be a factor but I doubt it, wouldn't make that much of a difference.
On the last oil change, I swapped to M1 0W40 because of the good reports I've heard on it and because it's about to be summer in Ga. Also figure that it's clearances have opened up a smidge.I will most likely go back to 0W30 on my next change-it will be getting ready for winter then.