Gasol + Randolph + Arthur are way better than Perk + Ibaka + Collison. It doesn't mean the Grizzlies are going to dominate the Thunder, but they have an advantage there.
Conley is playing better than Westbrook, IMO. Against the Spurs, he was too much for Tony Parker. We'll see how it goes. Conley (as every other player in the league) will have problems to defend Westbrook, but he's showing great team direction skills. That leads to great execution, while Westbrook has shown too little in the clutch.
The Grizzlies problem is the 2 and 3 spots. Durant is, by far, the best player out there, and the key will be if anyone can limit him, as he's unstoppable. The Grizzlies, although OJ and TA are playing great, are missing Rudy Gay and their young prospects are still too raw to make a difference against top teams.