I should clarify: overall, climbing Kili over 8-9 days is probably more of sustained effort than climbing Shasta. But in terms of 4-5 hour blocks, I didn't experience anything on Kili that was nearly as exhausting as slapping on crampons and going up to the Thumb in icy conditions, and coming back down (to be fair, conditions when I did Shasta were tough, and glissading was not possible). I believe that is 2600 feet in less than a mile; nothing compares to that on the nontechnical trails up Kilimanjaro.

On headaches, this was my first significant altitude headache ever, and it was a doozer. Frontal lobe, pulsing, and completely debilitating. An unambiguous warning that I could not ignore. On the bright side, I now know what to look for ... and avoid!