Well, I can relate my experience with using both organic store-bought milk, and raw milk from a local dairy (still normal hay-fed and maintained with vet medicine, but not GMO'ed or hormone'd up, local country doesn't allow it).
The Kefir from store-bought organic (pasturized, but non-homogenized) milk was fizzy, a weird taste, but good.
The raw milk I bought had a flavor in it after 1 day of sitting in the fridge of the smell of the barn where I'd go to tap it. As you know, likely, gut flora from the mother animal is passed into it's milk for the child, and that's what's pasturized against to prevent spoilage.
Making kefir from the raw milk simply intensified that barn-poo smell. Really intensified it, and I found it not pallettable. It'd perhaps be especially good for colonics (enemas) as probiotic implants, but for drinking, no, not really.