New
#11
Mostly because your hdd isn't loading textures fast enough, from the benchmarks I've seen single gtx 970 on that game is averaging 80fps in ultra/1080p.
Fallout 4: Graphics CPU Performance > Benchmarks: 1080p - TechSpot
Get an SSD to begin with and use it for the OS/Programs. And use the HDD for data storage, etc. Then you can tell if there is any improvement.
An SSD is your best upgrade. I would also replace the WD Green drive with a WD Blue or Black. The Greens are slow variable RPM drives and are best used for archival purposes. WD Blue will give you best performance per $$ and WD Black is the Enthusiast drive. Your 970 should be fine at 1080p.
I have a single GTX 970 and have no issues with fallout 4 (check my system specs). The SSD will make all the difference in the world. Your CPU speed should be more than enough.
Another GTX 970 in SLI will not give you dramatically noticeable improvements. However, if the upgrade bug does have you by the chips, and you are a game, consider the ROG series of motherboards.
A decent SSD is, as suggested by BunnyJ is all you need.
I agree, you are good on CPU & GPU, boot on SSD and store on WD Black.