Here's my experience, for what it's worth.
First, none of the boots most retailers like to carry fit me. After years of suffering, got a pair of custom Limmers years ago that were perfect, even though they weighed almost 5 lbs. Those wore out after several thousand miles, and later Limmers fit poorly. I did the "bootcamp" thing - a waste of time, travel and money. Tried two other custom bootmakers with no luck, and lost $$$ with one. What to do?
First, after 3 tries, found a good podiatrist, Matthew Burrell in Fryeberg Maine. Persuaded him to reluctantly prescribe and obtain a pair of PAL carbon fiber custom orthotics with reinforced blue Spenco footpads.
Next, since I already knew that Asolo, Merrill, and all the other brands most often found at EMS, REI etc. would not fit, I tried not quite so common brands like Danner, Zamberlan, Keene, Garmont, etc in the stores with my custom footbeds. I even found a pair of cheap ($30) Nevados that fit well, fair weather friends that have no water resistance. Whenever I go gear shopping, I bring along the footbeds and try them in several different brands.
I also use a "nine iron," or thick composite flat footbed underneath the orthotic footbed in the one foot that is shorter and has less volume. My feet are narrow in the heel, and splayed at the toes, so boots long and wide enough at the toes are cavernous in the heels, and boots that are snug in the heels crunch the toes.
So far, I have found several pairs that fit OK - not as well as my first Limmers or the raggedy Nevados, but they are sturdy and waterproof enough for treks.
Like the other posters, I have found that the lighter boots are easier on the feet, although I don't go for running shoe height as I enjoy dry feet if possible. Hiking with wet feet would also destroy my footbeds after a while. Good lightweight low W/B gaiters can help with keeping the feet dry also.
But most of the best long distance hikers i read about on this and other sites seem to go for the running shoe height, which must mean something. My own theory is that conventional hiking boots, by "supporting" the ankles, also limit ankle movement, thus putting unusual strain on the leg muscles and meniscal cartilage in the knees, which means pain, and for older hikers, serious damage.
But, whatever you believe, I agree with most of the other posters that if your feet are not easily fit, it is best to 'try before you buy.' When I do mail-order boots, it is with the knowledge that 90% of them will have to go back, and as with the store bought ones, they cannot be used outdoors until I am absolutely sure I will want to keep them. So, I wear them around the house in the evenings.
This all works much better for me than the outdated method of soaking the boots in a bucket and walking them dry.
I am hiking comfortably now, and the $400 for the PAL orthotics were worth every penny.
Sam Farrington, Chocorua NH