Penzoil is not the trash it was for many years. For that matter, all oils have improved greatly over the past 20 or 30 years. Penzoil uses the same process that Chevron does (they pay Chevron a license fee for it's use) It is also the same process as Texaco (owned by Chevron) as well as the same process used by Conoco (which also produces Phillips, Motorcraft, Union, and Kendall). Penzoil owns Quaker State and there is very little difference between the tow brands. Shell owns Penzoil. I don't know the composition of the current Shell product, but it has been traditionally a high quality oil. There is actually very little difference between any of the above oils.
The conventional (dino) oils have improved so much that there is no longer much difference in performance between conventional oil and synthetic oil. The main edge is in viscosity index range and extreme temperature use.
Actually, Mobil 5000 conventional is now using Group III base stock for their oil. Mobil does not recognize Group III as synthetic, but lost their lawsuit with Castrol over Castrol using Group III for their Syntec full synthetic oil. If Mobil 5000 had a Castrol label on it, it would be labled as a synthetic.
I too remember what trash Penzoil used to be, and still have a bit of a hard time in my mind about it, but being objective, it isn't bad stuff today. I'll probably still try to avoid it just from past injuries.
the 12,000 + miles on an oil change was my Vortech supercharged 3.8L in my thunderbird and I DON'T baby it. 
