770m and 860m are pretty much dead even as far as pushing fps. 770m comes out on top by a hair more often than the 860m though.
770m consumes 70 watts while the 860m consumes 45 watts.
a 256gb ssd is nothing to shrug your shoulders at though.
personally, i would probably go for the 770m+ssd, but that is me. you will have to decide for yourself.
power consumption can be considered very vital in regards to mobile computing.