It never came to my mind attempting supersampling on Crystal 
So I tested on 7800x3D, 4090, Crystal:
Resolution in OpenXR Toolkit 4700 x xxxx, DLSS Quality
- outside scenery - definitely crisper, less anitialiasing shimmering
- glass gauges - worse, especially text rendering - especially visible for black text on white background
- cockpit and steam gauges - probably slightly better
- probably better for steam gauges planes and admiring the scenery (VFR), this is my use case (A2A Comanche, no GPS, I use SkyDemon as my navigation app, running on the remote PC controlled via VNC inside All In One Tablet by Flightsimulator.me - the exact navigation software I use IRL), so I’m probably going to stick with this setting
Resolution in OpenXR Toolkit 3700 x xxxx, TAA 100
- outside scenery - not as crisp, antialiasing shimmer more pronounced
- glass gauges - definitely better, looks like DLSS is not soo good with text
- cockpit and steam gauges - probably slightly worse
- probably better for glass cockpit planes and working in the cockpit (IFR)
FPS - both cases more or less the same, in my case over Copenhagen (photogrammetry), FlyTampa airport, scattered clouds, FSLTL traffic: 36-40 FPS, smooth enough for me
I also compared original DLSS (nvngx_dlss.dll) v.2.4.12.0 with the newest one v.3.1.30.0. It may be placebo effect but I noticed very, very small text rendering improvement on the glass gauges, but I was also having the slight impression that the frame pacing wasn’t as smooth as with the original DLSS (despite ca. 40 FPS in both cases). So I reverted to the original DLSS provided with the sim, just to avoid any potential source of issues.
When I paid this stupid amount of money for 4090 and Crystal, I promised to myself: no more tinkering, just flying. And we are still tinkering. But I consider it a different kind of tinkering.
On i7-7700K, 4070Ti and G2 - it was like forcing MP3 player to not hurt your ears. You could make it acceptable, but newer truly good. Never like being in a concert hall.
On 7800x3D, 4090 and Crystal - this is more like tuning high end audio system. The differences are subtle, but the overal result is giving a lot of satisfaction. Maybe not like a real world concert venue, but with all the comforts of your own room.
@HugeMercury163 I can also observe the Crystal sharpness declining gradually when looking down. This is especially visible when I glance at my virtual kneeboard. So probably nothing wrong with your lenses.
@TjejKalas Thank you for your hint to explore supersampling.