EVGA has been changing up their OEMs and I'm not sure what's going on at this point. The original B1 was not reviewed well and so the B2, G2 and P2 were the ones getting all the recommendations. However, I did notice that the B1, at least in the 650 size went from a 5 year warranty to a 10 and have no way of knowing whether that represents their confidence in a better quality unit or it was just a marketing ploy. Since the change, there have been no published reviews that I have found. In some respects, you have to ask "Do you care ? " since you are basically guaranteed a working PSU for the next 10 years.
Right now, the EVGA B2 at $45 is pretty hard to turn down unless of course you are out to seek that very last few fractions of a GHz OC in which case the G2/P2 would be better choices. I'd also not that the 750 watter is a bit undersized if ya thinking you may at some pointy go SLI. On an air cooled system, 850 will do it if ya don't go too crazy on OCs....if water cooling ir using the Gigabyte 980 Tis, I'd suggest bigger,
http://www.ncixus.com/products/?sku=97531
I have a G2 1000 watter purchased because it was cheaper than the 750 / 850 on that day and was not too happy w/ it. The fan noise is bothersome and it's not just me as I have seen others w/ same issue on OCN. My current fav is the Seasonic Snow / Silent series.
As to the build.... is this stuff you cobbled together over the years or as currently planned ? rest assumes it's a plan
1. I can't make a case for an AMD based build with a budget over $850.
2. Big no-no on the 2 separate sets of RAM which are not guaranteed to work together. It works mostkly, but if it don't you have no recourse
3. I assume the SSDs / HD are existing either way...if not, I'd do single larger SSD and replace the HD w/ SSHD.
4. Recommend MSI, I'm not a fan of the SC series, the MSI Gaming, Gigabyte G1 and Asus Strix typically use custom PCMs with bigger / beefier VRMs.
5. Read and make sure you understand the implications of the EULA for Win10 ... many find the parts about using your PC as a download server and the "we can collect and distribute" anything they find on your PC disturbing.
To help ya decide, here's the relative value / ranking in order of fps per dollar of the various options:
970 - 3.97
970 SLI - 3.48
980 - 2.63
980 SLI - 2.30
980 Ti - 2.42
980 Ti SLI - 2.11