Well, it looks like PP has a hard time standing up to a turbo, at least in terms of it's shear strength...........Maybe all those molecules aren't so "adaptive" after all.

All joking aside, just because an oil shears out of grade, it doesn't automatically make it a bad oil. Heck, most conventional 5w-30's shear to a 20wt in 5K too.
That being said, if I were running a turbo car, be it OEM or after market, and lived in SoCal, I would run German Castrol (GC) 0w-30 which is a high 30wt (12cSt), Mobil 1 0w-40 which is a low 40wt (14cSt) or one of the "boutique oils" like Redline, Torco, Royal Purple, ect..
You should be able to find GC at any AutoZone, and only AZ. M1 0w-40 can be had at Pep Boys, WalMart, AZ, ect... As for the other oils, they are usually found at either race shops, or mom-n-pop auto parts stores, or online. RP can be found at PepBoys and AutoZone too. Amsoil is a good oil, but I personally am repulsed by their sales tactics, and would never use it, but that is just my opinion.
I would stay away from M1 right now, with the one and only exception being M1 0w-40. M1 is being thrashed around a bit right now, and on BITOG, there are reports of various WalMarts being ordered to send back all of the M1 because of a very quiet recall by Mobil............Real? I don't know, but something is up with M1, and it isn't good.