In reply to llanberis36:
I haven't had a pair of the mid-height ones. I did wear my old boulder X's for a 180km hike in Canada though l, because they were all I had with me, and really regretted it by day 4. The soles don't have much give in them, which never bothered me until then, but after several days the bottoms of my feet were pretty sore. It was also impossible to get them dry after they got saturated, and once they got wet the insoles scrunched up into a soggy mess. I ended up taking them out and persevering without insoles because I didn't have any other options. Added to that the sticky rubber doesn't stand up too well to long distances.
They're brilliant for what they're intended for, technical approaches, summer mountaineering etc, but not for trekking.