I have not tested, but I have the feeling that the peppershaker gives better outcome than the mill, maybe it is because the mill caps the pepper and does not average it, but gives the lowest grain Q and the shaker is only capped by the quern.
Maybe we get lucky and someone has some numbers?.
I use the empty containers in the table as symbel items and they give nice bonuses, and end up vanishing like the other items but take long time so they seem to me to be usefull. Ofc Im not an experienced player and still dont know how to combine symbel items and also I can not use gold or silk items, that must give better bonuses.