Now, let's compare another monitor. The BenQ RL2755 was a good monitor for its time, 1080p60 with low input lag , however compared to modern monitors it lacks high and variable refresh rate. 

First, let's look at PS5 SF6 RL2755 at the top. IDR remains on, which will be important later.

Results are 64ms, so only 7.4ms behind the PS5 version. 

RL2755 test at the bottom of the screen. 66.1ms, so 4.5ms behind the PS5 version on LGC2.

But wait. Did you notice something? At the top it was 7.4ms behind the PS5 version on LGC2, but only 4.5ms at the bottom. And it is only 2ms to get from the top quarter to the bottom, which at 60hz you would assume should take 8.33ms. So what's going on?

As we mentioned, this is a fixed 60hz screen with IDR on. Screen tearing is occurring. Essentially if the screen tears somewhere in the middle then the lower portion of the screen can appear a "frame earlier" than it does at the top. This results in the closer than expected results.

Is there anything else important to notice?

Some of the transitions on the RL2755 seem a little bit later than the LGC2. If you compare the left (LGC2) versus the right (RL2755) you could fairly make the point that the transition had already begun for the RL2755 on the left side, whereas for the LGC2 it hasn't. This would bias towards the LGC2, as it would have a slightly earlier recorded result. 

This is a reasonable criticism but it is not necessarily easy to overcome. The problem is the nature of the transition between the two different screen technologies. The LGC2 is an OLED screen, while the RL2755 is a TN LCD. As you can from these two screen the transition for the LGC2 is incredibly clear. Conversely the RL2755 transitions over 5ms or so. We could have set the threshold a bit higher, but the issues comes if you set it too high you end up with a lot of false positives. Later tests with the Alienware monitor have the threshold quite a bit higher (learning as I go). 

One last test before that though. IDR and screen tearing obviously causes major issues on a non VRR monitor. Is it worth sacrificing the screen tearing for a bit more input lag? These results are for RL2755 with IDR off. 

98.6ms would put it 34.4ms behind the same monitor with IDR on, and 41.8ms behind the LGC2. 

108.2ms at the bottom. For a 60hz monitor it should be about 8.33ms behind the top result, 9.6ms is near enough. If we were to compare the timing at the top of the screen, it would be 54.7 ms (LGC2 4k120 IDR VRR) versus 93.24ms (RL2755). If we were to compare the bottom of the screen it would be 63.7ms (LGC2 same settings) versus 112.39ms (RL2755).