Geoff from Microsoft, who usually helps out on the "WindowsMR" subreddit, posted some information in regards to the new SS Update, specifically talking about the Odyssey+ as he worked alongside Development on Windows Mixed Reality for SteamVR.
On a Samsung Odyssey or Odyssey+ headset (1440x1600 per eye resolution):
renderTargetScale == 1: Limit is 1657x2065 per eye.
renderTargetScale == 2: Limit is 2072x2582 per eye (this is the max; setting renderTargetScale > 2 won’t have an effect).
200% is 2015x2519. 210% is the closest we can get to that limit of 2072x2582. While 212% is true value, but SteamVR works in intervals of 10%, so setting it to 220% would downsample.
Source: https://www.reddit.com/r/WindowsMR/comments/a6cx67/i_found_a_way_to_prove_that_20_render_does_make_a/edkq6h7/?context=1
Keep in mind, the 210% SS feature is outdated and has been updated on SteamVR as of late July, 2019. For example, if you had 200% set, it probably was displaying the same resolution of the NOW set resolution of 140%.
This is why you shouldn't pay attention to the SS% number in settings (because it changes based on updates), instead focus on the hardware of the headset and select the highest possible resolution at a 2.0 rendering scale (2072x2582).
Also with the new update, you DO NOT need to mess with the SteamVR renderTargetscale settings in the log file. If you have the beta version opt-in, it sets that automatically to 2.0 for WMR.
This ensures the best possible quality without GPU downsampling... thus improving framerates and not slowing down Elite Dangerous.
UPDATE: This all being said, if you have found better settings for the SS or would like to mention any settings I've forgotten that has drastically improved performance or quality on the Odyssey+, please let me know. I'm by no means an expert and I'm basing performance off others experimentation because I hate messing with WMR as much as the next guy. Some settings I'm looking into:
• Messing with 3D Graphics Settings in the Nvidia Control Panel.
• Turning off Xbox Game Bar on Windows 10. Kind of pointless and wasting processing if your running Steam with a Live Streaming service like OBS Studio.
• Getting the Xbox One Controller to work flawlessly in SteamVR Home (So far no Luck). If you start up Elite Dangerous through that scenario, be prepared to turn on your WMR controllers to start the game.