1070 has a TDP of 150 W x 3 = 450 W
1060 has a TDP of 120 W x 1 = 120 W
total = GPU requires 570 Watt power then 750 W - 570 w = 180 W remaining power. Not to mention SSD, RAM, RISER that has not been calculated yet.
Slot draw (riser) is included in the card's TDP. The motherboard and the CPU draw less than 50 watts, not to say 20.
Most GPUs are heavily undervolted and draw about 60-80% of their rated TDP.
750W is perfectly enough for these cards. It will run at about 600W on stock load and 450-500W when undervolted.