I live in the pizza capital of the world (New York City)
and I'm extremely LI.  I find that I can tolerate a couple
slices of thin crust pizza that is cooked well-done from
an inexpensive "pizza-joint" if I take a few Lactaid
Ultra pills with it.  But I cannot tolerate thick crust pizza
that is not cooked well-done from a "gourmet" place
across the street from my office, even with lots of the
pills.  I think there are three factors involved: (1) the
type of crust (I think the thicker and fluffy crust has milk
in it), (2) the heat at which it is cooked (someone once
posted on this List something about how the intense
heat of commercial pizza ovens breaks down a lot of
the lactose in the cheese), and (3) the quality of cheese
(low fat cheese - more expensive - has more lactose
than high fat - cheapo stuff that pizza "joints" probably
use).

Hope that helps.  You just have to experiment (as long
as you are not  allergic-analphylactic).

Dave