As for myself, to answer the original question, best I have ever seen/measured is 7.8" BPEL, but since stopping PE a while back (now starting again), I've been closer to around 7.5" most days.
The funny thing is I've never seen many pornstars as big...only the truly big/huge guys like Mandingo, Danny D, Lex, Shane, etc. That said, I still don't really see myself as big, just around average to somewhat above.
As for lying about size...that's something I could never really do. If pressured I'd say between 7-8", which essentially is the truth, and thankfully still puts me above the '7 inch Internet average' everyone seems to be.