What gtx 1070 to choose ?

Hi I want to build my first ether mining reg and decided to go with nvidia gtx 1070 but there r more than 1 version of this card,so which will give me a decent amount of hash, say 25-30 mh. Another thing, i want to buy 6 cards but what if i don't find all 6, can i mix it with a different card say 1060 or 1080, i want to achieve around 150 mhs Thank u