Hmm I really see this fight going to BJ. But Sherk has a few factors which may really win it for him.
Here's my breakdown on why:
BJ obviously has the advantage in the jiu jitsu and striking. Sherk kind of reminds me of a LW Matt Hughes with better striking. Sherk actually uses a compact boxing style which works well for him and sets up his takedowns with his boxing. Alot of people say that Sherk's wrestling is better than BJ's but honestly in my opinion I don't see it that way. When Hughes and Sherk fought, Sherk's wrestling was pretty much useless against Hughes who was bigger and stronger. In BJ vs. Hughes for both fights, before BJ gassed and broke his rib, Hughes really couldn't handle striking with BJ and was barely able to take BJ down to the ground. So I don't see Sherk's wrestling as an advantage for him. I also don't see Sherk's monster strength as being totally overwhelming for BJ since BJ has been in the ring with both Hughes and GSP and strength wasn't a disadvantage.
However, Sherk has three things which is a huge advantage. His submission defense, he's never been submitted. Obviously if someone can, its BJ but so far noone has been able to. Kenny Florian and Hermes Franca couldn't do it. Sherk positionally dominated Franca for the entire 5 rounds. The second is his intensity. He's always going to be coming at you at 150 MPH. The third is his cardio. This is what allows him to come at you at 150MPH for all the five rounds. If BJ doesn't finish the fight in the first three rounds, I see the fight going towards Sherk as each minute goes by. BJ isn't known for his cardio although lately, he seems to have been taking care of that flaw. He may be able to go 5 rounds but going 5 rounds with Sean Sherk is a lot different. It'll really test his cardio.