So the "Software" Renderer always gives me perfect performance for the first level, but if I switch to OpenGL, it stutters and hitches like crazy. The ONLY setting that fixes the stuttering FOR ME is changing the in-game "Framerate Limit" setting to ***60FPS*** (I have a 60Hz Monitor). Besides that, I have V-Sync off in-game and forced it on in the Nvidia Control Panel. "Texture Mode" is set to "Filtered" (Didn't notice any performance change from "Classic"). "Anisotrophy" is at 16x, Palette Emulation is on, and I'm running at fullscreen 1920x1080 res.

I haven't tested performance for the full preview campaign yet, but when using OpenGL as the renderer, this "Framerate Limit" setting seems to totally kill performance with massive stuttering *unless* I set it to "60FPS".

Hopefully this will help someone, 'cause this is an awesome game so far and I hope the Dev optimizes it better in future builds/patches.

Windows 7 64 bit
NVidia GTX 980M
i7-4910MQ
16GB RAM
(Game was installed on a 1TB SSD)

That's interesting.

I also experienced some really weird stuttering and hitching and according to the GOG overlay my FPS drop in these scenarios to like 40 and below.
This happens pretty frequently in the first level in the outdoor area.
Afterwards in the second level it's not that bad anymore. But if the FPS count is correct, there are certainly some really weird FPS drops going on.

Regarding the settings:
I played the first level in OpenGL, 1920x1080, Frame Limit fixed to 60, Vsync turned off, Anisotrophy was set on 2x and textures were filtered.
So if I get this right, your tweaks don't affect the same problems on my side. But since my hardware couldn't be more different, I guess they don't have to. ;)
At first glance the game kinda runs better without a frame limit cap ingame for me, but this needs some more testing on my side.

My hardware:
Windows 10, latest patch version
i7 870
10GB RAM
AMD RX 460 (4GB)
Crucial BX200 with 500GB

In summary you can say, that the game definitively needs some more performance optimization with the opengl mode.
I didn't test the software mode though - gonna do that next. But I think I will get the same result.

It will be very good to know what version of OpenGL the game is using...

Someone linked a technical interview on the Doomworld forums and they are basically using the original Polymost renderer that was written for OpenGL 1.1.

https://www.youtube.com/watch?v=MHQv4mSG7_I

Is OpenGL 1.1 supported by modern GPU's or was it dropped?

I'm getting frame skipping up the wazoo. It happens alot on the first lvl, and when the game is mid-save. I've got a GTX 580, which may not be top of the line, but it shouldn't have these kinds of issues right? I'm also on Windows 10 with an i5

Any word on when the new update that just came out will be released on gog?

I am repeating here my post from the steam forums (but sightly adjusted):

I have also problems in both, software and opengl renderer. The software renderer is even worse. I stopped playing now, because the gameplay was running below 25 fps in level 2. The weird thing is that as soon as I open the menu ingame, the fps increase.

It seems that it doesn't matter if there is vsync or an fps limit active.

Heres my maiden.log: https://pastebin.com/kkErahbr

I hope that some further patch will resolve this or any configuration.
I have an Core i5-2500k, GTX 970 and Windows 7 64bit.

I was able to get 60 fps in the game, but only for some seconds when I looked at a specifiic spot or in an specific area.