Just yesterday, out of curiosity and without knowing that there was an update, I decided to give to the "next-gen update" another chance, after the first huge disappointment, and my surprise has been very pleasant.

The ideal would be to make a rigorous visual and performance comparison between version 4.0 and 4.01, however this is beyond me but these are my impressions about the latter, both in DX11 and DX12:

Before, my setup is:
GeForce RTX 3070 Gaming X Trio (overclocked and undervolted to 2070 MHz and VRAM to 7850 MHz)
Ryzen 5 5600X (overclocked and undervolted to 4.8 GHz and 84 PPT)
16GB RAM [from 3200 (16-18-18-38-56) to] 3600 (18-19-19-25-55).

• Booting has been normalized, the inexplicably long wait, which at least I had, no longer exists.
• The Performance option for the RTGI works, it makes it less heavy without apparently compromising the visuals.
• DLSS finally works, no longer the blurry mess it used to be, and it increases performance.
• The terrible pop-up, not present in the Classic version, has disappeared.
• Performance has increased a lot on DX11 getting closer to the Classic version.
• All of this, surely, is partly explained by and in turn is a consequence of lower CPU usage and higher GPU usage.

However, there are still issues, the main and most serious are:
• Processor usage continues to be very high.
• After a few minutes performance tanks, (I haven't been able to confirm a memory leak but I can't rule it out either).
• The performance tanks if any graphical option is modified.
• The fire coming from torches or similar, tanks the performance.
• RT Shadows are completely broken.
• RTGI sometimes has a very particular graphical issue (https://1drv.ms/u/s!AtMdKCR9hpeVgdYGf8Q_jvFJPHfnCw?e=UXbrzQ)

The game is already playable for me (at least before the performance drops) with: RT enabled, Global Illumination on Performance mode, Reflections and Ambient Occlusion by RT enabled; DLSS in Quality; HairWorks enabled, with AA x4 and High; and all major graphical options on Ultra+ (except for High on Number of Background Characters and Ultra on Foliage Visibility Range). All of this at 1080p and capped at 40fps (for stability, with dips in the mid-30s in the heavier parts of Novigrad).

I have to admit that with the mods, extra additions and the RT the game looks amazingly beautiful, however, there are still clear issues to be resolved.

I honestly thought the game would be forgotten on the despicable state it was left a few months ago but this update has given me some hope, so I really hope CDPR continues to improve it, it deserves it.

Interesting. I'm running a 3700X and if anything, processor occupancy is really low - it's only really hitting one or two cores. If they could do something to improve multithreading, I think the performance would be much better.

I have an R7 5800X (CPU) and an RX 6900XT (GPU). When the update first came out I was getting about 90 FPS with ULTRA+ settings and no Ray Tracing. After these so called hotfixes I get 31 FPS with the same settings. Even putting everything on low gives only 55 FPS at best. Something got really borked in the DX12 EXE. I hope they fix it soon.

How strange, I saw, as I said, just the opposite, an evident improvement although there are still many things to do.

Try to verify/repair the game files, then make a backup and then delete the game folder in "C:\Users\User name\Documents\The Witcher 3", boot the game locally (without GOG Galaxy) and set it up again (you can copy the "gamesaves" folder to the new folder to go to any particular saved game). The point is to configure the game from scratch, avoiding any conflict with previous options.

Repairing/verifying the game seemed to fix nothing. It is running the same. I usually repair a game before posting about technical issues. Reason I did not was because I had repaired it the previous patch (4.00). Does not seem to matter either way.

I do agree that there seems to be some more work to do. Come on CDPR, get it together and forget about all that ESG crap. Focus on what matters.

I'm still intrigued as to how you're about the only person worldwide who reported high CPU usage in the Next Gen patch (on a not terrible processor with a decent number of cores).

Everyone else who has been complaining about performance has basically seen what looks like CPU driven bottlenecking from low CPU usage/terrible or non-existent multi-threading beyond two or three threads).

Check out my RT optimalization guide, it may help you improve performance:
https://forums.cdprojektred.com/index.php?threads/the-witcher-3-ng-4-01-rt-optimalization-guide.11112433/

I don't use Galaxy, but I can confirm that a fresh install (removing all settings files as well) made zero difference to performance.

Thank you but following the guide the Foliage Visibility Range on High is very ugly, the particular increased Grass Density of the update is lost and, above all, the massive performance loss (supposedly due to a memory leak) is still there and the performance gain compared to my configuration is very little.
I prefer the graphical fidelity to the maximum capping the frames at 40 to avoid stuttering

No, I'm not the only one at all, even Alex Battaglia from Digital Foundry has said so (15:32), and his video is after my post.
I don't know if I didn't express myself well but the point is to compare the CPU usage on the Classic version versus the 4.01 with unlimited framerate, that's what I mean.

Video: https://www.youtube.com/watch?v=VNWmo_WeGSU&ab_channel=DigitalFoundry

You don't have to use thoes graphic settings at High if you don't like it, go to higher option. But for you GPU i recommend to change AF settings in Nvidia CP - point 1) of my guide and install RT mod ini - point 7) or mod ini from from point 8).
Just try it: The Witcher 3 NG 4.01 - RT Optimalization Guide / Memory Leak Fix

Weird. I hadn't seen those videos. I would expect higher (better) CPU usage on the Next Gen version as it should work better with multiple cores. Does seem that it interacts differently with different setups.

My problem is that CPU usage is low on a 3700X, which is causing my 2070 super GPU usage to come in at 80%. Basically, the game on my PC isn't utilising the CPU properly which is then causing a CPU bottleneck. GPU usage should be between 95-100%

Well, in the end I only used your 3rd (cloth simulation), 4th (GPU scheduling), 5th (HairWorks) and 10th (CFG) steps and only changing the Grass Density to Ultra: I gained about 8 fps, now it's capped at 48 fps, so I gained 20% performance without compromising the visual quality.
I doubt that the external tweaks have helped, but just in case I used them, although you were right about the HairWorks, they are partially broken visually and on top of that they consume a lot.

Thanks somehow.

Great that's helps u improve performance but for what point if you didn't even try to fix biggest issue in this game from point 1),

Wow, that in turn seems weird to me.

I would like to diagnose your case but it is a very complex issue.

What we can at least agree on, it seems, is that the game in its current version and state is broken.