It's interesting to me how this conversation draws arguments about Peter's postion and authority and against the R.C. Church. That just clouds the question, UNLESS the argument is in essence ad hominem [that's meant to be a descriptive, not an evaluative, phrase] and goes something like "The R.C. Church is full of lying, neurotic, superstitious fools, and has been since the time of Ireneaus and Tertullian. Consequently their evidence is of no weight."
I think the argument could be plausibly offered with respect to Tertullian. Anybody who could write as wittily as he did about "'Christians to the Lion' What? So many to one lion?", cannot be all bad, IMHO. But I know of no a priori reason to think that Ireneaus was incredible.
So we have one credible early witness to an even earlier "common knowledge" that Peter was in Rome. What is there in the "against" column except the strong desire of some that it not be true, so that every possible suggestion that the RC Church might somehow be the Church in its fullest can be discredited?
But as I and others far more worthy and important than I have said, the question of where Peter was is a different question from what his vocation was and what the Church is.
We have a direct command from the Lord to not go among the Gentiles. [Matthew 10:5-6]
Does this qualify?????