Adding a second GTX 780 won't give you a %100 increase in performance. More like %60~70 with the latest drivers.
As for FPS, You didn't mention the software or settings, but on average you can increase the performance of a stock GTX 780 by %15.
Sorry about that I made a mistake saying double lol. I wish it did double the performance. It gives you more FPS for sure. I have the eVGA card so precision is what I have and some reviews have been able to push the card up to 22%!
I see what you mean, however, according to the review, the unit seems to increase efficiency after burn in. Also, they stated that after the burn in the rating is very close to 80+ Gold. The thing is: I am wondering whether or not Corsair will be willing to take this unit back on the grounds that it is not a true 80+ and doesn't have specified continuous power output and exchange it for something bigger which I am willing to pay the difference. Or, should I just sell it and get the platinum series?
rule of thumb baseline per card uses max-peak 40 amps on older cards newer card 35 -30 amps
so match up a PSU that has the real numbers on 12v rail not the combined BS advertised
burn-in is for silicon gets better not wire wound coils. you have or not also they loose over time
Your AX850 is perfectly fine for two cards, but yes you would have to upgrade if you wanted to go up to 3 cards.
Remember I have the same PSU and have 2 580s and have my 2600K OC'd at 4.8GHz. Now when I have everything maxed out, my UPS shows me hitting about 750-800W and there are two monitors plugged into that UPS as well. Also I only ever got really close to the 800W mark was when I had the 580's OC'd up to just past 900MHz and the cpu was at 5.1GHz. So if mine could handle that you can handle the two 780's as they draw less than those 580s would have been.
"Nothing sucks more than that moment during an argument when you realize you're wrong."