Simple answer is he would lose. However I think BJ is training with Aldo for the Edgar fight. I don't think he would ever fight Aldo. I'd love to see some training vids though. Would be a sick addition to the fight pass!
Penn fans will be disappointed. Aldo would outclass BJ. I don't understand the comparison. Aldo is faster, has better cardio, with vicious leg kicks. Penn is at twilight of his career. Don't get me wrong. I like watching Penn fight. But he has nothing left to prove, so why continue? He will always be one of the greatest LW champions of all time, with welterweight title on his resume. But at this juncture, Penn does not have what it takes to beat top UFC fighters in their prime.
I think, therefore I am. - René Descartes
As you think, so shall you become. - Bruce Lee