i would run exactly what the factory recommends until you feel your car is good and broken in. DO NOT run synthetics like Royal Purple and such during that break-in period as it may not lube the engine parts correctly and you could cause damage to pistons and whatnot.
I have found with my other cars in the past, (I use my other cars as guinea pigs to test new products and anything I am curious about before appling to my Impala,) that if you go from synthetic to conventional oil its a bad thing. My 93 subaru didnt run smoothly after that. I was working as a field tech and was driving 45,000 a year, so I was changing my oil every month. I went back to a synthetic and it ran better.
Our BMW has magnets inside the pan of both the trans and motor. You'd be amazed the amount of metal those magnets pick up. Every time I change the oil, I take some metal off the magnets. I buy magnets now and put them inside the pan of EVERY car I own, to get what the filter doesn't.
I use, and have for years, 10w40 valvoline in all my small block chevys. I've found it to be about the best in my experience.
Ok, I have read this thread and read around Bob is the oil guy site. When should I start running synthetic in my new Impala? I have run synthetic in my 2000 Chevy Silverado 5.3L since I bought it (it has 32000mi on it when I got it so this wasnt an issue). I was thinking running the GM Goodwrench (or conventional Mobil) until after my 15,000mi oil change then switching to Mobil 1 Synthetic on the 3rd/4th oil change. Is this a good thought process?
The problem with synthetics in a new vehicle is that they work SO well that they will not let the engine wear and break in. I would say wait at least 10,000 miles before switching. I have heard of people getting better mileage up to the 10K mile mark. That tells me that it takes a car about that long to break in properly.
However, I run non-synthetic in my 2003 Cavalier. According to the owners manual I have to change the oil every 5000 miles otherwise I void the warranty. After my 100,000 mile warranty expires, that will be very soon, I will use Mobil 1 and change the oil every 10-12K miles.