Specific armor bonus viability? (Dodge vs. Evil ex.)

[Styxwash]

I was wondering about the viability of items with armor bonus vs. specific types, like Dodge boots vs. Evil +4 or Natural Necks vs. Slashing +4.

I know these properties are supposed to work just fine in general, but I heard that they can stop working at some point if you have alot of attacks hitting you at once?

Vs. Evil should be the most reliable type, but what about Slashing? Far as I recall, most high end epic monsters and bosses deal Slashing damage or are of Evil alignment, or even both most of the time.