In your locaton, you would be hard pressed to see any measurable difference in wear between those oils and the intervals you listed.
Realistically speaking, the 3,000 mile interval is dead. I change our conventional at 6-7,000 miles and using syn in my mother's car (currently PP), I change at 10,000 +/- miles.
Additionally, the current cost difference between the two is minimal. If I did not have a stash or was not able able to acquire conventional at the deals I find, I would simply run Pennzoil or Quaker State Synthetics.
Just to touch on "severe service" intervals, the used oil analysis of my trail Jeep at 1500 miles (which is MANY hours of trail time!) is more severe than ANY street driving most people encounter. The TBN was still strong and Blackstone recommended running 2,000 more miles. I now run these rigs out to two year change intervals and have fun worry free.