Ok ya'll here is my $.02 worth. I run Castrol 20-50w (live in south Ga) pretty much year round in all my vehicles and change it about every 3-5000 miles. I owned a vehicle with a 4 cyl. engine and around 125,000 miles the radiator came apart and the wife continued driving till it stopped (the rings were cooked and the pistons were scarred). I rebuilt the engine and outside of the damage that was done when it ran hot the inside looked brand new. You could still see the cross hatch on the cylinders. There may be better oil out there but I run the Castrol. I am also a big van of John Force and his sponser is Castrol.
As ya'll know though the secret is to change it often.