I've always wondered about this issue myself. Reading the responses here has been quite informative and educational for me.
In my vast video collection, Cody James ("Big as they come #1" video) has the cock that reaches furthest past his navel. He has a huge cock, though it is cut and crooked.
James has competition but the models are anonymous so there's no point writing about them here. Also some pornstars/models are never videotaped so that the navel distance is an issue.
Probably Cody James, who is tall, has a relatively short distance from crotch to navel, but having one of the longest cocks on video certainly helps. Bam is probably as large, but only reaches about 1" above his navel, whereas James' cock goes about 4" past his navel.