So setting the bearing scar test aside.....I'm surprised the Platinum flowed SO poorly in the cold in both his cold tests. That's not okay.
The additive packages being so much lower in the Platinum than the two cheaper "conventional" Pennzoil samples....I'm wondering....Is this a case of the Platinum being "made from natural gas" needing less detergent additives because by its nature it does not need as much? Same for the lower "anti wear" package? Since neither of those lubricate, are you better off with less detergent and "anti wear" additives if the oil does not need them? Honestly asking, thinking out loud.
BTW, I have a 2007 Xterra with 261,000 miles on it, owned since new and it has had Pennzoil Platinum 5w30 every oil change since new with a Fram Ultra filter, both changed every 5,000 miles. Runs as new, starter replacement is only repair to drivetrain. At 244,000 miles I replaced the valve covers and was stunned at how clean/new the top end looked. I took a pic. I can't find the original, but I did find where I added a pic I found of an Xterra at 89,000 with poor oil change history and sent the pair to my daughter to get her to see why its important to change your oil. My engine is the one on the left.