My opinion is that if you're interested in running your oil for extended periods of time, you need to look into taking samples and getting them analyzed.

I have a 2005 Honda Civic that is our "good gas mileage" vehicle. The manual calls for 10,000 mile oil changes for normal conditions and 5,000 mile oil changes for severe duty conditions. I was dubious so I changed the oil every 3,000 miles for the first 4 or 5 months that I owned the car. Since I started taking a sample and sending it in for analysis at every oil change, I have worked my way up to where I'm going to run this oil 8500 miles. I'm using the cheapest ($10.50 for a 5 quart jug) Quaker State oil I can get from Wal-Mart (except for the last change when Wally World was out and I had to substitute the second least expensive oil which was Penzoil) but I do pay for the most expensive Fram Filter they have. I'm not saying I love Fram Filters, I'm just saying it's convenient to get stuff at Wal-Mart and I'm afraid of getting the cheap version if I'm going to run the oil that long.

If you research it a little you will find that some engines are much harder on oil than others. My Civic is supposed to be fairly easy on oil. I would imagine most newer cars are not much harder on oil. The only way you will know how well lubricated the engine in your car is after many miles is to take a sample and send it in for analysis. Here is the last sample I got back on the Civic.