Something tells me that if your Chevy has a 6 quart sump, and you put one quart of each of the top end synthetic 5W-20 oils - Pennzoil, Mobil-1, Valvoline, Castrol, Quaker State, and a wild card like Supertech, your engine is apt not to know the difference. Granted, that's NOT a recommended practice, but just sayin' that the differences between the top brands of the same weight and grade (all things being equal) are so slight that it comes down to either personal preference or price.
Some folks get in a rut because they've always used a particular brand, and that's okay. If it ain't broke, don't fix it. However, your Chevy might run a bit quieter, or start easier, or get better oil life out of one brand over the other. Finding that sweet spot is half the fun (and most of the expense).