EDIT: Updated Facts and added DCSv2.5 bench. o7
I want to continue huge work done here but also focus not on fps but on frame latency.
Like most of you already know frame latency/frame render times are much more important than pure average fps. With all stuttering and inconsistencies of DCS engine and DCS maps it's frame render time most important statistics. For those who play DCS with Vsync because they don't like stuttering or play in VR it's even more important. For VR every frame has to be pushed by CPU in 11ms time window (90Hz) and for 60Hz monitor it has to be prepared in 16ms window. If not - this particular frame won't be rendered and fps will be cut in half to 45fps(VR) and 30fps(60Hz monitor vsync). Of course i'm omitting g-sync etc.
Facts to be aware of:
1. Fast frame render times and good frame consistency is what people perceive as a sense of flying and flying speed. That's why BMS is regared as very good at it - it's just old as hell and has very low frame latencies on modern hardware.
2. In case of VR or Vsync you can have CPU utilization at 40% and GPU utilization 100% and be CPU bottlenecked. It just means your CPU can't push all the data for a frame in 11ms - it doesn't have to be utilized 100% for that. It just will not make it in time.
3. People tend to think that if CPU is 100% utilized on every core Game engine is well optimized - it's the opposite when it's done with work on 30% utilization and waiting for new task it's much better optimized.
4. Yes DCS Game Engine (mark difference between game engine and graphics engine) is CPU bound not GPU bound (less truth in new v2.5 in non VR scenario). Of course you can throw at it 5x supersamplng, 8x MSAA, 5x DSR and much more and you will push the GPU to it's limits (hence 100% GPU utilization in the point 2 above). But when you set lowest settings and start mission you can be restricted by your CPU power because those 11ms and 16ms restriction and it will bottleneck your system.
5. It's highly possible you will have average 70fps with those frame drops and stuttering because fps measurement is just a statistic - temporary fps or average fps but just a statistic. Useless in case of stuttering, flight feeling, fluidity and all of what I focus on here.
6. VR asynchronous time warp/asynchronous reprojection help much in case of dropping to 45fps but will break flight feeleing and in case of infrequent drops it will be unpleasant stuttering of game objects (not your view).
7. In VR if you drop to 45fps your head will still move with 90fps(see above) but ground and all objects inside game will move 45 fps (every second frame) - hence frame jumps and stuttering. Most of it when you fly fast and look sideways (not in front of you) at the ground.
8. Even if you don't use Vsync or VR all of above affects your fps quality (BMS example above)
9. After all tests I lowered my CPU speed from 4.7GHz to 4.0GHz to see what diffrence it will make. I've got about 0.5-1ms more on every test maximum in v1.5.8 tests.
10. You should turn off any affinity bullshit from autoexec.cfg (if you edited that). It can ruin CPU frame time consistency (increase frame time variation). Leave it at default auto (all cores).
11. While testing I changed process priority to HIGH for DCS.exe, vrcompositor.exe, vrserver.exe to decrease frame time variation. I don't recommend setting it to real time because it could impact input latencies or make game unstable (I crashed couple times). But all in all helps coz Windows 10 wants to do every unimportant action while I want to squeeze every ms from rig :doh:. I'm not utilizing CPU 100%, just want to be sure DCS will be first in line. If you use oculus remember that setting DCS.exe higher without oculus rendering pipeline processes can make DCS slower not faster.
12. testing GPU and CPU frame times is the only proper way to tell why those frames you have don't give you expected flight quality. Only way to tell if you should have new hardware. Only way to know if this new CPU is worth the money or not.
13. Someone asked me important question Why do I turn off terrain shadows and cockpit global illumination in prefered settings if it had no impact to performance?
It has impact on performance - just not on CPU frame render times. First you need to take care of CPU if it makes in time with frame data than You want to max out your GPU potential but not overload it and make it in frame time. All in all i can't have 11ms in VR so I'm choosing lower than 22ms variant for both CPU and lower than 22ms for GPU.
14. I wanted to know is if it's possible to use DCS without stuttering in 90Hz in VR with current existing hardware. If it's possible - I leave this question to you.
*I measured the impact of the DCS graphics settings on CPU frame render times VERY roughly with Steam frame statistics tool while running DCS in VR. Every game graphics setting was tested with ALL others turned off or lowest possible. I've chosen two Su-25 missions which struggle to give good performance on my rig even on lowest settings. I tested simplest possible scenario standing on runway in VR in singleplayer. If this struggles with stable frame times and asynchronous time warp/asynchronous reprojection kicks in than more complicated air battle or multiplayer wont work with stable 90fps. Measurement was done in cockpit (simulation was of course started by clicking start mission). Intel speed step turned OFF and all of possible sys settings to high performance. My CPU is 4.7Ghz watercooled and it's always 4.7GHz without any boost/ jumps or anything. My Rig is in my footnote. With hardware I have i'm not GPU limited but CPU limited. I hope my work will be useful to you. I will update it with 2.5 stats.
DCS 220.127.116.1118.311 - in VR
DCS 18.104.22.16816.422 - in VR
DCS 22.214.171.12418.311 - in VR
DCS 126.96.36.19916.422 - in VR
DCS preferred settings for VR