The skylake CPUs supports both DDR3 and DDR4. This means that it's made for both DDR3 and DDR4. It's up to the motherboard manufacturers to chose which one.... DDR3 mem for a CPU made for DDR4 ...
Only a HDD and no SSD,DDR3 mem for a CPU made for DDR4,windows 7 while microsoft went ahead to only give proper support to newer chips in win10.
Still it would help to give us a concrete example of how many fps you get in a certain game/settings.
Also make sure to disable any and all power saving features from the bios ,nvidia control panel and from windows control panel,just to make sure everything runs at full power.
