I had 12.3.6 for about 2 days now, on two cars, a model S and a model Y. Both comes from 12.3.4. I took 4 trips, about 1.5 hours each trip, about 30 min city and 1 hour highway.
I feel .6 has minor improvement over .4. v12 is major improvement over v11. Ever since I am on 12, I don't remember...