It really comes down to the overclock on the 980Tis. Overclocked 980Tis are about 300W, so your whole system with the OC CPU and everything is probably looking at about 850W precisely of power consumption.
Seeing as the 850 B2 is a high quality PSU, I expect protection circuitry to work very well just in case you do overload it. How cool the PSU stays also plays a major role in this.
Overall, yes I this should be sufficient, but pushing the PSU to its limits. UNder gaming conditions, you system will probably be using enough current to merit 650W in total, so you should be perfectly fine. Your system probably will not see stress as bad to get near 850W.