DayZ Stress Test #17, 18, and 19 had much lower FPS for a lot of people, compared to Stress Test #11 for example, and I might know why, and a potential fix for it. TheRunningManZ (twitch streamer) was complaining about the FPS drops, and in a tweet, he figured out and showed the issue and potential fix.

TheRunningManZ's tweet, "This evening was way better BUT my CFG file has set the render res to double 1440p. (more than 4k). When i set it correctly it was better." 5:51 PM (PST) June 1, 2018

Apparently, there's a supposed CFG file, that isn't being updated correctly, and is making the render resolution higher than it needs to be. This could be one of the reasons for lower FPS in this test compared to other ones. Having the render resolution be doubled, than it supposed to be, can cause really bad performance.

I also have a pretty good PC (SC2 Hybrid 1080TI GPU, Intel Xeon E5-1650 CPU, 16GB RAM, ...), and I was 60FPS, dropping to even 40FPS; When I was getting about 110/120 FPS on Stress Test #11 (I'll include my specs too)

Also, someone's render resolution was Render_W=2553 and Render_H=1436 when they're playing on 1920x1080, and that can cause unnecessary FPS loss.

So, look into this CFG render resolution file, that isn't being updated correctly, that can be causing major FPS drops.