1070 sli

I've got a pair of GIGABYTE GeForce GTX 1070 N1070WF2OC-8GD cards (https://www.newegg.com/Product/Product.aspx?Item=N82E16814125875) I would like to either sell them and use the money to buy a 1080 Ti, or find someone that wants to directly swap. They've never been overclocked beyond whatever...

So i did a major upgrade over the winter with intels retail edge winter deal. Picked up a 6850k Msi Krait mobo 32gb ddr4 corsair vengence led 2x evga ftw gtx 1070 hybrid gpus 256gb m.2 ssd off course i have more storage thats just a boot drive. Now yheres my question do I go 2k or 4k only...