This still doesn't explain that having 150 FPS vs 84 FPS would reduce input lag, which is what I thought your original point was. He does mention that v-sync will create some lag.
I have those fps-drops with big fields and certain places too... with approx 150fps alone on the track, my PC still stays over 110fps when there is 20+ racers and we are doing those tough places like Moss.
I have theory about neverending discussion about 'changing grip-level between Qualify and Race-session'... if you have noticed that debate. It might be just because most peoples fps drops down when there is full grid, and that leads to situation where they miss apexes because those increasedmilliseconds of latency. It feels like changed grip-level when you miss corners just littlebit, but I think it actually is caused by those inches what you are more far than usually, what you see on your screen. It ain't needed to be much to miss inside curb and slide so wide that you cant get good exit. That was my problem too, when I tried to keep 'high-settings' and thought that 60fps is max with my 60hz screen.
I went back to that thread where my friend tells some details about fps and latencies. Here is some facts he tells: (hope it makes sense... I Google-translated it, and did some corrections)
"If the simulation is running 30 fps, it means that one image goes through machine calculation of approximately 33 ms. The image data are 34 ms old already at the stage when the picture shows on your screen. If the screen draws the image on the screen as it comes in, the bottom image is 34 ms old , and top 50 ms when the old drawing has been completed (and this is optimal). If Vsync is on, you can add to this delay a one frame, ie the delay is a total of 50 to 67 ms.
If the game runs 60 fps, single frame calculation is approx 17 ms, and without vsync-delay from 17 to 34 ms.
120 fps (in 60Hz screen) to calculate a single image takes about 8 ms. Since the screen can not be updated than only 17-ms intervals, this happens so that half of the screen image is 8 to 17 ms old and half of 17 to 25 ms old (ranging from the lower and upper range, and because sync is not perfect, the line moves all the time). The disadvantage of the picture may appear disruptive tearing, when first half of the image is different image than the second half.
240 fps in the picture is 4 parts... 4, 8, 13 and 17 ms old.
120 Hz screen (as long as the fps is more than 120), these delays can be further halved."
So in a nutshell, if you are running steady 60fps, and I'm running 120... I have half of that latency compared to you. Different thing is, if you have better 'inner prediction-code' than I have, so you can adapt to latency even without knowing it. I think this issue bothers more those guys who drive 'with their eyes' more than those guys who 'drive the game'. I'm definitely one of the first guys. I also think that to become Alien, you need to be in that second group.
I know I have too much fps, cause even my lcd-monitors latency is more than my fps now... (well actually it's 5ms, just checked... so it's not) but that's just mental thing. I like to see that I'm no where near 120fps when running, so my pc ain't struggling.
Edit: So that we could see these milliseconds in real perspective, I made some simple school-math in my head. Correct me if you find bugs... I used to be quite good in these some decades ago.
Example: Youre driving long straight with 240kmh speed, and starting to get close to your brakepoint.
240km/h = 24km in 6minutes
24km in 6minutes = 4km in 1minute
4km in 1minute = 400m in 6seconds
400m in 6seconds = 40m in 0,6seconds
40m in 0,6sec = 4m in 0,06sec
4m in 0,06sec = 2m in 0,03sec (30ms)
It's easy to see that when youre trying to hit perfectly to apex, if your car actually is two meters more far than your eyes says... it's going to be 'hit or miss' lottery everytime before your 'inner prediction code' learns these changing things. For you, the problem aint so bad than for me. You are used to steady 70fps, so youre braking two meters 'too early' because that's how you have been learned it. For me, if my fps drops to near 60-70 range, I will shoot almost something like 1meter over my usual inside-line, and then wondering what happened to grip-level.
EDIT: hmmm... I feel that I hijacked this thread with my speculations.
I dont know, but if OP feels that way too, it might be good to move these few posts to iRacing-thread. There they might be easier to those to find who also are iRacers. This thread might be better with only those great videos... though these posts started from one video, so someway they are related to topic. Your call Berkeley!