I might not be understanding this correctly, but for the viper set, for both the 2-item and 4-item benefits, it says "adds 4% weapon critical". I assumed, because it was listed twice, that this was cumulative (ie wearing 2 items would result in a 4% crit bonus and wearing 4 items would result in an 8% bonus, which sounds pretty darn good to me).

Just replaced an old armor set with 4 viper pieces and I'm only seeing a 4% increase in weapon critical...is this as it should be or is something not working right?

And if it really is just a 4% increase, why is this benefit listed twice?