On shoes: I used light hikers, Lowa Bora GTX, on a non-snowy hike last year, and loved them, except for the rocky parts in between Trail Camp and the summit. At that point, I developed foot fatigue, and wished at times that I had a stiffer sole. However, it sure was great hiking with a lightweight, comfortable boot that did not cause blisters (for me). I realize the conditions are different now, and crampons are probably required for some sections, in which case this type of boot would not be appropriate. I am currently breaking in a light mountaineering boot (Scarpa Charmoz GTX) for a first attempt at Shasta next week.
On Diamox and AMS and speed of ascent: our group consisted of three 40-something women. All three of us were first timers, and all three made the summit. However, the two of us on very low doses of Diamox (62.5 mg) who went up slowly did not get AMS (and we both had voracious appetites at the summit to boot); the third woman, who was not taking diamox, and who went up quickly, did get AMS (I believe she started feeling poorly near Trail Crest, and was downright sick the summit, and did not fully recover until she was below 13,000 feet again). Yes, altitude is an individual issue, with serendipity also playing a role. So I share this anecdote for whatever value folks may, or may not, find in it.
Also, I do not believe that the fact that someone who has been to 12,500 on one or more prior occasions without problems necessarily is a predictor of how they will do at 14,500 on a different occasion. Indeed, the woman in the anecdote above had, before getting AMS, (1) spent two nights at 10,000 feet, and a third night at 12,000 feet, and (2) successfully climbed to Kearsarge pass a day before we hit the Whitney Trailhead (just shy of 12,000 feet). Prior sleeping altitude, speed of ascent, level of hydration, and the weather (warmth factor) are among the many variables that may affect the likelihood of getting AMS (in addition to genetics/personal susceptibility).
