Evidence suggests that e500s go on PA for all elite members. Miles from 1P or lower are apparently the only upgrades that go on PB, as far as I can tell.

That said, I have no idea about if you put in a Pending request as a 2P, whether the system will recognize that you are a 1P and confirm/waitlist the request at the 1P window. Personally, if the request will be Pending anyway, I would wait until after you turn 1P, just in case. The time at which you go Pending doesn't really matter, since the request isn't even officially considered until the window opens.