Main bearings remain the original factory bearings with 60k miles on both Darts. Rods bearings were changed since the originals were at max clearance. for both Darts.....maybe SL-6 may wear the rod bearings faster then the mains?

You have a lot of inexpensive, easy things to do before you pay any heed to a spurious assertion that your bearings are shot.

With nice fresh bearings such as you describe, 10w30—even synthetic—is on the too-thick side of things for fast oil pressure on cold start. Try a switch to 0W30 (I use Castrol Syntec) and see how that does. I found a noticeable improvement in oil pressure speed on startup even switching from 5w30 synthetic to 0w30 synthetic. Don't be afraid of oils that would have been considered unreasonably thin in the past!

We switched my daughter's Dart to 0W30 (...) There was no discernable knock so Dan gets a thumbs up for this recommendation!

At what temp do we switch back to 5W or 10W?

Cold ambients generally run high 20's to low 30's F in the winter.
The oil pressure switches are screwed into the oil pumps for both Darts. Rod clearances ran .001 for both Darts.

The beauty of two identical Darts: theory of relativity applies & helps reduce the human judgement factor. When there is a distinct performance difference then it points to something that isn't identical. I'm comparing both cars at the same ambient with the same oil & filter so it might be some of the things raised outside that loop. Changing the oil for both Darts to a lower viscosity sounds like a good idea for the winter.