Like eric said approach/departure/breakover angles are what keep you outta trouble. Those increase with tire size increase and lift.
Flex is important, but only cuz it keeps the 4 wheels on the ground. When you're locked on an axle and you pick a tire, you still get 3 wheel drive. A good flexy wheeler can go pretty far with open diffs (since it can keep all 4 on the ground).
When off road, IMO traction is king. Tire choice for the terrain, keeping wheels down, lockers, all get you that. If you're high centered, you loose traction, if you're open diff and pik a tire you loose an axles worth of traction, tires load up with mud, you lose traction ...