I started using synthetic in 1982. Converted a number of carb'd gasser big and small blocks over the next twenty years.
On the CTD -- even in hot as Hades South Texas -- the motor turns over from cold just that much easier with synthetic. I've been using T6 Rotella and a BALDWIN filter. Change annually the past few years as miles have been quite low.
I agree that dino is worlds better than thirty or forty years ago. And that the gap is smaller. THe vehicle is a keeper so oil change cost is irrelevant in main.