Machida & Anderson train together so i doubt they would fight each other.
i don't know about 7/10, but i would give BJ Penn a great chance in the rematch. it would all come down to BJ's conditioning (shocker ). in the first fight, GSP was able to get him down because he leaned a tired Penn against the cage. BJ clearly won the stand up battle between the two. BJ is really the only person i've seen make GSP work for a takedown.
i would probably lean more towards Penn if they were to rematch, because i believe he would come in much better conditioning.