I run Amsoil 5W30 full synthetic. I only put on about 15,000kms a year; the oil is rated up to 40,000kms/yr so I change the oil on the same weekend every year to keep things simple.
I don't use the car to tell me when to change the oil. Not to argue but that's like my tires telling me to fill them to 60psi, when the maximum pressure the wheels can handle is 50psi. As far as computer tech in vehicles has come in the last decade, I still prefer at this point to rely on the tried and true methods of vehicle maintenance. I do like the OBD system for narrowing down problems in vehicles unlike the carb systems of yore which left you with a slew of testing should something be amiss.
GM knows cars. They pour BILLIONS of dollars each year into vehicle research. They designed the OLS based on this research. It is meant to stop you from changing your oil when you don't need to. Their goal is to reduce the amount of oil that gets wasted every year.
If the OLS sensor isn't telling you to change your oil, then there is no reason to change your oil. 3000mi/5000km intervals are too frequent and are nothing but a waste of oil.
Yes the Synthetic in those tests was run for 15,000mi. There were some LS1's that were run up to 25,000mi (!!!) with only slightly more contamination in the oil than there was at 15,000mi. They recommended 15,000mi oil changes because they didn't think they'd be able to convince people to run with 20,000mi oil changes. Even regular dino oil will last a lot longer then 3000mi. Some manufacturers recommend changing the oil on their cars at 12,000mi intervals (with dino oil).
This is one of many reasons why GM went bankrupt. Spending in areas that don't require them to do so when they can just state a 7K oil change interval instead of 3K and make that the standard across the line.
A lot of people don't realize that 3K oil change intervals were the norm before overdrive transmission were on the market. This decreases engine wear by a good 35%, and higher power engines, not to mention tighter machining tolerances, that require less cruising RPM lowers that 35% to the 50-60% reduction range in engine wear.