I have a graphics card that can run Garry's Mod all on High with the texture quality on Very High and with x8 Anti-aliasing, other than that, i didn't do anything fancy, i just no-clipped into the room way past the map's limit where there is a bottomless Breen model that does the Breencasts on the screens, i did use Simple DOF and adjusted it so that it blurs the background and not Breen, i also used the Camera tool to zoom in so that background covers the screen completely while making sure Breen stays in focus
Also, while using the Clean Up Everything button, i noticed the Breencasts broke, they were distorted in a vertical stripey kind of way, like you'd see bits of Breen's face as well as bits of the Combine logo that shows up when Breen is done talking, i don't know if it was like this before or after using the Clean Up Everything