About as volatile a fight as you'll find. Both have the power to hurt the other guy and neither has some proven Ivanov-esque chin where they'll be shrugging off the other's shots consistently. That being said, in Pavlovich's loss to Reem he didn't get dropped and never went fully out. Overeem took him down with a sweep, trapped him against the fence from top position, and managed to land several solid GnP shots that hurt Pavlovich until the fight was called. So maybe a slight durability advantage for Sergei? That's iffy though.
Sergei has the reach advantage, youth, and wrestling to fall back on hypothetically, but he's yet to use the latter in the Octagon... hell, after the last fight Derrick might even shoot on him. Lewis has, IMO, better timing with his shots and far more experience.
Could honestly see it going either way, but regardless it's going to be a KO/TKO within the first two rounds IMO.