Proviron and testosterone (any test, including prop), are a very nice synergistic stack, pretty nearly an "ideal" stack of an oral and injectable, because both drugs will actually act to enhance the effect of the other.
You´ll have more of the test you shoot as free testosterone because Proviron reduces SHBG, which binds free test... ultimately more free test = more muscle-building ability..... and you'll have more androgen receptors to be bound to by the Proviron (compliments of the testosterone). And while this is debatable, since Proviron binds pretty strongly to AR's in fat cells, it may contribute to lypolisis (fat burning)