Excuse my lack of understanding. I don't know what T-stop means, and I am only guessing at CPl lens. Would that include a "G" rated lens?
Thinking back to that day of shooting, I guess I assumed "metal object + high sun = glare. That's why I put the polarizing filter on. Of course the metal had many curved surfaces. So the the polarizer at any particular setting would only minimizes a fraction of those.
On a straight sided car, such as an older Rolls Royce with those long, flat doors, I could expect to gain something.
You have probably heard that relatively new saying: To man holding a hammer, every problem looks like a nail.
I spent $100 on a new B+W polarizer and wanted to use it. Here are the EXIF files of the T-Bird and Corvette.