I usually recommend 850's for twin GFX setups.....doesn't the Asus moBo come with Asus probe ? That should give you all the voltages you wanna monitor. But a true test would be to download OCCT and run the torture tests for CPU, GPU and PSU and look at the graphs afterwards (assuming it passes) and look for any dips.
My PSu stays between 12.14 and 12.02, so when I see 11.46, it seems a bit low....which Corsair is it ? The TX isn't supposed to get that low:http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story2&reid=73