M0SIE

Core voltage runs the GPU, in other words the electrical potential of electrons flowing in the GPU's compute cores.
 
whether you should touch it depends on the cooler and PCB.

Core voltage can allow you to squeeze out more performance but not necessarily.  Also Nvidia Pascal GPUs have a lot of protections in software so as long you know what you're doing and don't disable these protections it's nearly impossible to break the GPU by giving "too much" core voltage, the GPU simply won't do it if it could possibly damage it. 
 
 
From my own testings on a 1060 it's a pretty useless feature as it may improve test results in benchmarks (at +100%) but in games the GPU will throttle exactly the same with +0 or +100,  there's literally no real world difference except it's more stable without a core voltage OC, which might depends on individual games though. 
 
 
So,  really,  if you don't know exactly what you're doing *do not touch the core voltage*  whatsoever,  it's not worth the risks, however small they night be. 

Yes. That says that m2b only supports PCIe SSDs. You'll need to install your SATA SSD in the other slot.

Driver : LINK

pushed my HDMI cable even more didn't move at all

Either should work with your Setup / PSU.
 
780 Ti has slightly better performance at the price of being more power hungry and less "futureproof" regarding driver updates etc.
 
i would personally go with the 970 (that being said keep the vram thing in mind)