Lesnar has a 7" reach on Fedor, which is pretty significant, especially with about 40 lbs added. Whoever is going to take out Lesnar will need some KO power and a good reach. This way they can try to avoid the take down, otherwise they have to come in too close.
But IMO the only way to beat Brock is to hope he makes a wide open mistake and go for the submission, ala Mir/Brock 1st fight. Problem is, the more fights he logs in, the better he gets.