GM’s oil life monitor is supposed to be the best around. If you want to do some research on how well it does the trick, poke around at http://bobistheoilguy.com
Many people have this system and have sent in oil samples for analysis.
Myself, I work in a high-tech field and drive a 17 year-old car without an oil life monitor. But if I had one, I don’t know how much I’d trust it. If the monitor says I have 20% life remaining on the oil, what does that mean? Does it mean the oil is protecting a lot less than when new, but is still acceptable for most driving conditions? Does it take into account the quality and grade of the oil you put in the thing to start with—No. Does it account for any make-up oil added? I’m not sure, but adding a quart of make-up oil in between changes when needed significantly increases the life of the oil. Would I want to drive 90 MPH on a hot summer day with oil that had 20% life left? Probably not. If I had 20% of my fuel left, I’d be looking for a gas station right away. If I knew I had 20% of my life left, would I be taking it easy in the hope that I’d last longer? Deep questions…
I think I’d stick to 3,000-4,000 mile intervals with a good dino oil or if you want to push your luck, use a good synthetic and go 5,000 or further. Send in a sample for analysis if you’re curious–it’s under $25 to do so.