Faith Gratz Oriold, a former SMF member, experimented a lot with cream soap. She and I got to comparing notes a few years back. She wanted to develop a formulation that didn't have the disadvantages we're talking about here. She mentioned this --
"...I have done many experiments with low to no stearic acid up front and no to low stearic acid as a supercream and they all start out fine but eventually want to turn translucent and lose their opaqueness...."
The last I knew, she had given up on finding her holy grail of cream soap.
I saved a comment from another cream soap maker who said her goal was 50% stearic in the recipe. (I would suggest the goal of 50% combined stearic + palmitic.) If you can get that high with butters alone, using butters alone is certainly an option.
I think due to cost and availability, most people opt for using commercial stearic acid sold for B&B products. This "stearic acid" is actually just over half stearic acid with the balance being palmitic, FWIW.