I agree about about said rx 570 or gtx 1060 is much cheaper and profitable if you compare the price and hashing power..  like the above said there are some algo's has different speed if you buy higher specs like gtx 1080ti or vega 64 they have algo that you can mine much more faster gtx 1070 or 1060 they have algo that they are much greater hashing power than you are staying in one algo of ethereum.