Apropos the previous post about ArtForz’s GPU farm, I exchanged some emails with Stephen Gornick who apparently tweeted about this almost 4 years ago (here and here).
Below is an image of ArtForz’s ArtFarm. Notice how you can visually identify 20 GPUs. At its height he used 24 and it is unclear if these in the image were all 5970s because he mentioned having several others (including several 5770s and a 4870).