Patman, I could not have said it better myself. You would make a good Pennzoil salesman
Here is the main difference in the three oils mentioned above. First of all, they all use the same additive package except for what I will list.
1. Regular Pennzoil: Group II+ base stock with about 80 ppm of moly.
2. High Mileage Pennzoil: Group II+ base stock, which has a slightly higher viscosity index than the regular oil, 80 ppm of moly, and a very small amount of esters for seal conditioning.
3. Synthetic Blend: 88% Group II+ and 12% Group III. No moly.
For my personal applications, I use regular Pennzoil 5W30 in my Nissan, 10W30 in my Pontiac 3.8, and I use our European Formula Synthetic 5W40 in my wife's VW Eurovan.
I change the oil between 3,000 and 4,000 miles on the regular oil, and I change the synthetic between 5,000 and 6,000 miles.