OMG not another oil thread!!
I love oil threads.
Oil with high zddp content can do 5K miles.
Oil with low zddp content should do less than 5K miles.
People who rationalize by saying "I've been using a low zddp oil at the factory recommended interval for years now and have had no problems" are simply saying their engines do not YET show symptoms of engine woe. There was a letter to the editor of Excellence magazine this year where this issue was specifically addressed and the engine expert answering the question said they are seeing a lot of problems on engines that had low zinc oils like mobil1 left in for longer than ~3-4K miles. They advocated for oils with ~1350 ppm of zddp or at least 1250 ppm.
Seems to me that If your oil has this, it will typically boast about it. If it doesn't disclose it, probably a reduced zddp oil. This is probably why its getting harder and harder to find out who has how much. This is important because its not so much the zddp level going in, but how much was left when the oil came out.
so if you save on buying a reduced zddp oil at Wal-mart, inherently its a short life span oil. Not worth the savings imho.