Personally, I think Forrest's best chance of winning this fight is to work really hard on his guard and submissions.
I believe Robert Drysdale is his jiu jitsu coach. If I'm right about that, Forrest should easily be able to submit Chael from his back if he really works hard on his guard. He's bigger and maybe stronger than Chael. He's got really long legs (which REALLY helps improve submissions from the guard.) And most importantly, Chael's sub defense has been his biggest weakness throughout his career.
Planning on submitting someone of your back might sound like a risky strategy, but I actually think its a good idea in this case. Forrest should obviously continue working on his striking and takedown defense. As I see it though, his striking is already better than Chael's and there is no way he is going to improve his wrestling to the level of Chael Sonnen's in a single camp.
This is how he should be thinking:
Plan A: Defend the takedown and pick Chael apart standing on way to a UD.
Plan B (because plan A has a good chance of failing): submit Chael from your back. He's certainly got the skill and the instructors to make this a reality.
Forrest has decent td defense, but I think Chael runs through him. Gotta think Chael will be able to mirror what Ortiz did to Griffin their first fight. I say either Chael via UD or tko in the later rounds. Forrest is just getting run down, while Chael still has some gas in the tank. Chael should be the stronger fighter come fight time. He's still a big lhw, and I have to imagine his gas tank will be solid without cutting all that weight.
This fight is interesting but i could have thought of better.
Griffin is stylistically better then Chael in most areas.
Striking edge to griffin
BJJ edge Griffin
This fight could go down many ways, Griffin doesnt have the best chin so Chael could just test it and use his wrestling to keep it standing, chael has a great chin and Forrest is not threat to KO even a 2 year old so dont count out that he may chose to stand and take shots to land some for a KO.
He could take it to the ground and GNP.
Forrest is more skilled then CHael but he has no chin and no ko power intresting fight.