You need to power up half a level in order to try and check it, but even then it's not conclusive in some cases due to the stat distribution of Snorlax. If the final CP at full levels is the same, the IV doesn't really matter.
In any case I'd advise against powering unless it is a Lick/Hyper beam, Zen headbutt/hyperbeam or Zen headbutt/heavy Slam.