First of all, if you are meaning to make an accurate replica, khopesh were cast from bronze. If historical accuracy is not a big deal for you and you just want to make a knife with that form then I would see about getting some 1065 or 1070 if you want to do a hamon which is also foreign to these weapons. Of course 5160, 1080, or 80CrV2 would also make a good blade just not a good hamon. I don't know if I would go to the really high carbon steels for a blade that is basically a chopper unless I was keeping the size down. Some khopesh were not terribly lone blades.
Doug
