The problem with reflections is not flickering but a SSR delay of a few frames. I guess the frame number is the number of gpus and maybe is related with "reflections_delay" variable that is into the game executable. That glitch is more visible in fast camera movements, in my case I play with a controller so is barely noticeable and worth the rise in performance.
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There are a few spots where SLI scaling is wrong in Metro 2033 Redux. You can fix it using custom SLI bits 0x080F12F5 instead of defautl 0x080000F6.
