With the caveat that everyone reacts to altitude differently, in general, many folks who have altitude issues on the Whitney Main Trail (if they are going to have altitude problems at all), usually begin having them somewhere between Trail Camp (~12,000') and Trail Crest (13,600'), as they are ascending the 97 Switchbacks. There are always exceptions, of course; but this generalization seems to fit what happens for many people who do encounter altitude problems on that trail.
CaT
Let's see, I've tossed my cookies at June Lake, Whitney Portal, Chickenfoot Lake, Saddlerock Lake and have reached various peaks over 10,000' without any AMS related problems...including Mt. Whitney and the 9 nine peak of the SGW one weekend.
Sometimes there is no rhyme or reason...you just get waylaid or have a great time. That's why, if I'm spending a bunch of time over 8,360', I will do the Diamox thing.
