FYI
The amount of time/mileage that a motor oil should be used before it's changed is not just based on how long it's base stock or viscosity can hold up before break down.
You must consider two things that naturally occur which can take their toll on the oil as well as the engine.
1. Although an engine oil with a stronger base stock, film strength and superior lubricating characteristics is better able to shield moving parts from the naturally accumulation of dirt and contaminants, over time/mileage this is still a serious concern.
2. As mileage increases it is normal for small levels of fuel vapor to get into the crankcase and mix with the oil, over time this accelerates the break down process of the oil, dilutes it's remaining viscosity level thereby reducing it's ability to properly lubricate, if left long enough this can effect emmission levels causing other issues.
All oils are subject to the above two results if used for too long of a mileage period, three to five thousand miles is the the maximum that I would suggest leaving "ANY" oil in a daily drive before changing it and the filter.
A quality synthetic oil of your choice supplies better viscosity durability, film strength, heat resistance (less likely to coke) and much better lubricity than organic oils but recommended oil and filter change intervals should never be exceeded regardless.
