If Serra could beat GSP then Story sure as hell can. Story imo will be GSP's biggest challenge in a long time if they are to fight.
Story won't let GSP fight safe. He will make him brawl at least a little bit and likely will be able to push him up against the fence a couple times.
Story is a huge WW and is well rounded. I still see GSP winning though as he has better takedowns and gas tank as well as is a faster and more technical striker. He is also a far smarter fighter.
nobody is ever gonna make GSP brawl, making him strike is possible but not brawl that is a mental thing and GSP won't go there.