Correct. You would have to externally record off of the output of a DP/HDMI/DVI port.
Oh 🙁
But can you benchmark them using fraps? 🙂
Does it have to be AMD? Nvidia Shadowplay works pretty well at 1080p with little to no performance hit compared to DXtory or fraps.
I'm only speaking from my experience with Shadowplay. I don't currently own a Mantle capable AMD card.