From those Stat GPU screenshots I only see that somehow post processing and unaccounted is higher on DX12. Is it due to a CPU bottleneck? Maybe it’s due to Async Compute? I don’t know, as stat GPU isn’t the best tool for such investigations. Certainly DX11 being faster just due to RHI or drivers would be quite unexpected.
you’re not attached. don’t you worry. it’s not personal or individual.
i just don’t like your test methodology, tho. fps pea nuts is so pc, but it’s worthless in the broader spectrum, being consoles that can handle lumen just fine if you wouldn’t ask for all those frames.
a lil balance the engine has to have. 
I can go deeper and give you an profiler output if needed. Again this has been tested across AWS G4 Cloud GPUs, steamdeck, 20 series cards and GTX series cards. You really start seeing gains on 30 series cards which is why I mentioned Ampere chipsets.
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I only put fps there next to the ms for easy reading. Nobody and I mean nobody over here is looking at fps… that stat doesn’t mean anything. If you look at my performance percentage calculation it has nothing to do with FPS its a reduction in total ms from each pipeline and shader model. Again, I think your swaying around the purpose of my efforts and missing the entire point and directing your feedback towards me personally while saying your not.
I’m at a loss to more clearly outline every other stat shown on those screenshots other than FPS especially when Memory Footprint and RHIT were in bold? 
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@Krzysztof.N on a side note … what I just realized these systems have in common. AMD CPUs and chipsets. Is there something you guys are tracking internally around differences here DX12 vs DX11 performance on AMD vs Intel? Could there be an AMD specific issue between the RHIT when running DX12 that isn’t seen on Intel chipsets/CPUs? You have me intrigued now. I’ll do similar test on my Intel chipsets and get back with you… Pretty sure the AWS G4s are Cascade Lake however and still get better perf in DX11 but they are non RT Radeon V520 GPUs (running lumen SWRT)[Granted this is UE5.1 mind you as 5.2,5.3 had webrtc memory leaks]
Update:
I did some searching around to see if others regardless of CPU/GPU setup are in the same DX11 camp and found this thread. Again case after case of ppl toggling back to DX11 with a mixed hardware setup.
Appears this is the culprit still
Attached is a really quick Trace you can attach with insights if you’d like to review. (DX12 SM5 UE5.5)
20241118_173420.zip (24.1 MB)
Can this Lumen problem with DX11 and UE 5.5 be solved, enabled, with some workaround?