Noise Margin

Hi,
I'm working on characterizing io cells. I thought of measuring
Vih,Vil,Voh,Vol. I'm confused with which method to follow. In some
papers its said, negative unity slope method gives pessimistic results.
The better method would be Maximum square method of measuring SNM. For
io cells, had anyone done any analysis of this kind. I'm intersted in
sample spice decks for measuring SNM using MSM.
Also, in -ve unity slope method, does anyone know any in-built hspice
commands for measuring -ve slopes/directly Vih/Vil. As I need to run
for around 375 corners, I need some automated way of measuring these
parameters.
Also, I could measure Hysterisis in Schmit trigger inputs, but any
automated way/measure commands for measuring Vih,Vil,Voh,Vol is there?.

P.S: The io cells are not single inverters, they are composed of more
transistors.
Any help is appreciated.

Regards
Prakash