Any comment about below Performance tunning idea?

[Carfield Yim]

We have a form calling

List.contains()

a lot of the time to check if the user have permission to view / amend
difference fields. The visibility checking process is somehow complex
and it is not easy to simpify, but according to the benefit result,
this is the bottleneck that form.

I just wonder, can we using sortedlist.contain() can improve this part
by N to log N?

[Cerebrus]

Maybe the EqualityComparer is taking time ? You haven't told us what
the "List contains" !

SortedList is very slow during adding/removing items because the
entire list is resorted (in addition to checking for uniques), but
better duing searches.