I use the comparison of erection in side view with the side view of the pelvis area to guess how big porn stars are.

I am average height and build and in side view my penis is just under 1" smaller than the pelvis side width which I measured at around 9.5" (most guys of average build must be between 9 and 10")

John holmes and Mandingo's cocks are clearly on the "bigger than" side of this relationship.

Omar's looks equal so I'd say 9.5"

I saw him putting his cock in a pussy whilst Rocco Siffredi was already inside and they looked about the same size. Rocco's 9.5" is quite honest I think.