He gets rock hard... while inside her. Very short session, so I believe you when you say he fucked several sluts before this was filmed. His climax was pretty huge here. I counted 10 ejaculations. They all hit her mouth, but that doesn't make it any less powerful. Lots of volume.
The curse of being the top male performer in the industry. You'd think to maximize the performance they might stretch production by a day or two to not over work talent. Despite that, Peter still manages to give a performance sexually better than what about 90% of other guys can do on their best day. You got to give the guy credit where it is due.
You could tell Pete was off his game for this scene, it's later in the day so this was probably 4th or 5th scene of the day. His cock wasn't as big and stiff as it usually gets even as she nurtured his cock in her mouth and his cum shot was average, just a few sputters. He looked overworked and stressed out as he prayed to the sex gods that his cock would not go limp before the cumshot.