Don't let the flex fool you, the Kaiju can easily handle any free riding you throw at it. Vermont, Maine, Utah, Colorado, pipe, park, steeps. I don't know about bigger terrain like AK etc but Nicolas Muller rides them all over the world. However if you "prefer" the feel of a stiffer boot the Ion is a click or two stiffer. But I find my Kaiju do everything just as well as my Ions and leave me feeling a little more mobile and unrestricted in my movements.
Nice! You say the toebox felt wider? Was there more space to the top of the boot in the toebox too? I'm thinking about picking a pair up but I have enough room in the Kaiju. I like how the toebox in the Burton Ions is "flatter" so you can pressure it more easily when lifting your toes up in a turn.