drop in FPS

[Mrkite]

hey guys I recently built my first PC geared towards gaming so I'm very new to this. I have a MSI twin frozr 970 GTX GPU, with an i5 4690k processor. I recently downloaded Ryse son of Rome since it was just on sale this weekend at first it was running smooth but then I started to get lag especially when engaged in fight sequences. I have traps running and it is steady at 59 - 60 FPS then will drop into the 20's topping out at 30 when the lag begins. Like I said I'm new to this but I thought with my build I could run games like this no problem on high settings with 60+ FPS, I may be wrong though. I'm trying to figure out what causes this lag and possibly fix it. I've been researching overclocking too but right now being new to it and not wanting to mess anything up I'm going to keep researching that until I'm comfortable knowing I won't try my new pc. I also ran crisis 3 on my build running 58 to 60 FPS. Thanks for any help.

 

[Mrkite]

Meant to add a link to my build http://pcpartpicker.com/p/hXGKgs