The past strikeforce event showcased Overeem's dominance over Brett Rodgers. He made QUICK work with him and it could've been faster if Overeem utilized more kicks (leg or head). Overeem has great gnp, wrestling, jiu jitsu and PHENOMENAL striking (K1 fighters have the most finesse in their strikes).
Overeem IMO will be the guy to take Fedor off his throne. I don't see how Fedor could match Overeem's technically sound striking or ground game, not to mention the reach, height, weight and strength advantage. Fedor of course can never be counted out but I see Overeem taking Fedor out.