Steve: Anytime I tried to plow in heavy trash or sod without coulter they would plug much more easily it seemed. I wish I had know you had coulter to sell. They will bring fairly good money here.
Part of that maybe that we are not as dry as you. The trash here is many times tough because of the moisture in the trash. Also we like to have a much smoother finished plow surface than what it seems is common where you are.
I just know I have had a couple of sets of plows without coulters and they did a terrible job compared to the plows I had with coulters.
The top picture is more of the finish we usually want/have around here. The bottom picture is from your area and seems rougher. I think it might also be the soil types as well.