Maybe 31 feet. I don't know. But I do know there's more involved than the physical part. Unless you get some great mutation, the size of lungs and heart will limit you. You are limited by the makeup of the human body.
Improved facilities are a factor, too.
John Lucas, professor emeritus in the department of kinesiology and sports history at Pennsylvania State University, agrees with Bannister and Beamon that records will continue to be set - for a while. But not forever. The long jump has been stalled for six or seven years. That doesn't mean we're near the maximum. We have come to a troth at the moment.