I'm late to the thread as well. I find this is highly personal; much of it has to do with the shape/slope of the last. The wrong last and my feet are killing me even if it's a kitten heel. The right last and I can do 3-4 inches no problem for hours on end. Otherwise, I have short toes and my feet are wide at the base of the toes, with bunion on one foot -- opposite of your issue.
My feet do not like the Sofft brand. Since your feet sound more narrow than mine, I'd recommend trying Cole Haan. I love their shoes but they are just a smidge too narrow in the toes. They do have a lot of cushioning.
Another favorite is Camper:
http://www.camper.com/en/eshop.....38;smax=42
Unfortunately I don't care for all their styles, but some of them are pretty cute. I have a pair of Campers in which I can stand, walk, dance, pound city streets pretty much all day long without blisters, cramps, pain ... nothing. The secret is in the heels: they are made of some very forgiving squishy stuff. Give them a try.
ETA: These are very similar to my Campers! Except without the tassle. And in a lighter shade -- more nude than beige. I've had them for two years now and they've held up well:
http://www.camper.com/en/eshop.....=21682-001
Otherwise most of my heels are Via Spiga. It's like that brand was made for me. I wore strappy 3 inch Via Spiga's to stand around on a cement trade show floor recently for 8 hours with no issues. I also do well with Aerosole's. Nine West is hit or miss -- cannot do the taller heels but the mid-range are decent for 4 or 5 hours.
Stuart Weitzman is great too. And Franco Sarto. My feet love that brand.