Unless you are desperately in need of gold, never convert trooper, eternal or lilith frags into precious souls frags. They are worth way more to your game as sac fodder. Counting on precious souls for gold or sac value is a waste.

Only convert left over frags from events into precious souls frags


Iron coins come from trooper, eternal, lilith and alchemist souls. That source of iron coins from souls have become less important than IC drops from other places or rewards. As you progress in the game IC becomes more readily available.