Quaternoin difference. (Tolerance for out of sync)

My multiplayer has jittery objects if I just put a rigidbody in the "observed" of a network view.

Making a prediction system looks hard. . . So my idea is to just have the server instantiate all the rigidbodys except the player and periodically send an rpc so clients can check if their copies are "good enough" , otherwise snap all parameters to what the server sent.

I am using the square magnitude for the vector3's but.. . I dont understand quaterions. . How can I check the difference between 2 rotations in a meaningful way..

Converting to a vector3 would loose rotation data so I think that would let some out of syncs go completely undetected.