honestly it doesnt matter if it is 6400dpi or 10,000,000dpi. once you get to a certain dpi threshold you will not see any real improvment. i usually set my mice up at anywhere between 900-1500dpi, even if they are capable of 5x that number and i do fine. having too high of a dpi setting can pick up the micro twitches in your hand.
if i remember correctly the mamba is the wireless mouse razer makes. the deathadder is their basic corded model. for around $100 and $50 respectively both are way overpriced for what they are. with that said, the deathadder is functional and the build quality seems good enough to get at least a few years out of the mouse. the only issue i have is that the rubber surface is a dust magnet and can only be cleaned with water or other inert liquid.