Comfrey Bocking Variety Differences

Both Bocking 14 and Bocking 4 comfrey are listed as the "preferred" variety for compost, what exactly is the difference between them? While I have you here, what soil requirements do they have, will they do ok in a clay soil?

Bocking 14 is recommended for medicinal applications while Bocking 4 is recommended for animal feed applications. Bocking 14 is high in allantoin the cell proliferant agent that helps healing. Bocking 4 is high in protein.