What you describe about dlss vs. TAA making not difference makes sense if the rdrthread is the bottleneck. Perhaps you know about this, but in any event here’s a useful post describing this situation (hopefully it’s creditable). Not a very hopefully situation, but it’s something that we’ve all been dealing with in MS FSs for years: no computer is ever powerful enough 
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I’m not running SU4 beta, but there are reports that it noticeably improves VR performance. I might give it a try, but since having a messed up beta experience with 2020 I’m hesitant to do so.