Even two blu ray videos cause lag, but I am not surprised.  I use it for only one monitor and mostly content creation, so I have a mic, drawing tablet, DAC, and it can handle all my applications like Blender, Krita, and Helm.  1080p 60fps youtube playback on one screen (or two if mirrored) is smooth and nice, don't expect steam games if they are better of on a 4,000$ gaming machine.  Visuals novels, emulators, and browing the web work great on this machine, I use Linux Debian.