The extra height of the OR will not be noticable. If you thing you may getting into some fun situations... get the OR. If you have a hard time getting dust inside the X, dont want a single scratch on any bumpers or cringe at scraping your frames on rocks and stuff... you are not ready for the OR, so get the S.

The S is capable of taking you places that will scare the average person. If you have taken vehicles offroading and actually know when/how the locker, then get the OR. Otherwise, the S will be just fine.

On the topic of needing a transmission cooler... I have no experience and welcome someone else to pipe in.