Camtrip :
What do you guys think of this one? How can I decide if it's good quality?
http://pcpartpicker.com/part/seasonic-power-supply-ss850am
Dear, when it comes to PSU, pl remember this is not just cost but an investment to safe guard the other components of the system. There are two things with PSU one is Load and the other is Stress. In order to make it easier all that you need to check is the efficiency of the PSU. To help things out, 80+ certification is there but it is not necessary that PSUs not having this certification will not work.
AX760 is 80+Platinum which means it would be giving you 95% or above efficiency theoretically. If you've budget go for AX800 series. In my view AX760 will be enough for your GPU. For SLI go with 800+W.
Always check the 80+ certification reading (Platinum, Gold, Bronze, Silver) and the efficiency. You may also consider sound level of the fan in terms of dBA.
Happy Hunting!