Like I mentioned on the other list....
My Sidis give my toes cramps after 45 minutes. My S-Works last me all day. :)
I'd venture to guess that among good cycling shoes, they are not
"comfortable" or "uncomfortable", they either fit or don't fit. You
want a shoe that fits. The one that fits me might not fit you. Fit
is a function of the footbed and the insole. You can try different
shoes. You can try swapping insoles to improve things with a given
shoe -- if I put my S-Works insoles in my Sidi's, they are pretty
decent. You can also buy thermoformable insoles to customize your
fit, though I think those are pretty bulky. There are also companies
that will make a mold from your foot and produce a custom insole for
you. I haven't tried that but the folks I know who've done it love
it.
A good bike shop with a good fitter should be able to help you with
all these things if you don't luck out with a shoe you love (like I
did with my s-works).
eric