3:50 - 3:52 clearly shows you are correct about length. Her hand is longer than his dick. When she grips as the scene continues you her hand on his cock. Measure a woman's hand or the average man's. That cock can't be more than 5 1/2" long.
Sorry to burst your bubble, but Blaq Marq could rarely get it up, and could only last a couple of minutes. And it's not obvious, but he was only around 5'4" and 130#. Chiseled as hell though.