The Arreat Summit gives some information on this. I'm not sure how much of this is correct.
AFAIK, there is no limit, so you could theoreticly get 100% CS or DS. They do exclude each other however, so you will never get 4x damage. Magical/elemental damage types aren't effected by CS/DS, only physical damage is.
Edit: Corrected: attack = damage type
AFAIK, there is no limit, so you could theoreticly get 100% CS or DS. They do exclude each other however, so you will never get 4x damage. Magical/elemental damage types aren't effected by CS/DS, only physical damage is.
Edit: Corrected: attack = damage type