afaik gtx 1660ti will be a equivalent to gtx 1070 in performance, as it is already said that is 20% faster than 1060 6gb.
GTX 1660 will be a downgraded version of the TI, which is my opinion is just a rebranding for another 1060 card (performance related).
GTX 1650 is the same, another GTX 1050ti rebranded.
It will all depend of prices. if that GTX 1660ti is around 250$ at most with 1070 performance, then it can be a good deal for tight budgets.