Once again, the order means nothing becuase ALL of the books are infallible.
First, the Pope is NOT the only infallible authority of the Church. All of the Bishops in unison (the Magisterium) are also infallible, and can make infallible proclamations. The Pope is the only individual member of the Church who is infallible, however.
Second, the Pope is only infallible if he is speaking ex Cathedra (to the whoel church), on an issue of faith and morals. Just because he writes something does not make it infallible. He has to specifically make it an infallible pronouncement. The books of the New Testamant have nothing to do with Papal infallibility or Magisterial infallibility–they are infallible because they are the inspired words of the Holy Spirit. So the fact that Peter’s letters are not placed first in order does not mean they are any less authoritative, and the fact that Paul’s are placed first do not make his any MORE authoritative.