bicycle_repair_man :
Completely agree with RobCrezz; the GTX 760 will be drawing so little power that a 660W PSU will be perfectly capable.
Out of interest, why use a GTX 760 just to run the desktop? Does your CPU not have an iGPU?
Wait wait wait. Hold up. So how does this work, I was under the impression that I needed the 760 on the extra monitors to get the performance of a 760. Is it truly working as an adapter to add more monitors and running off the 780ti? If so, I already have a GT210 in my machine alongside my 760. When the 780ti comes should I just take the 760 out completely and replace it with the 780ti, leaving the 210 to deal with the extra monitors?