Ingots will be as clean as seller was willing to clean them. Like anything else some folks do it better than others. Melt a few of the ingots in a pot, junk will float on the surface of molten lead. Should give you a good idea of how clean the ingots are from your supplier.
I think range lead is going to be the "new" wheel weight. Since non-lead WW's are becoming more and more the norm the range lead is fairly consistent, can be harvested by people and resold for a profit for a reasonable price.