Most of the time i got 40fps~

specs:
AMD 3700X
GTX1070
16GB Ram
Win 10

Have you turn on complex shadows? I did so and had low FPS. When I came back to simple shadows it worked fine (and didn't look much different).

didnt fixed it. :/ Still low fps

The Problem is the ddraw.dll wrapper from gog in the dungeon siege installation Folder. I have deleted ddraw.dll and have full 60 FPS. i Play it on a Amd Vega 8. With the ddraw.dll wrapper i have low FPS too.

i will try it out. Thx bro :)

I had low FPS too in DS1, after install. In the installation folder is a prog call DXCFG.EXE. It will allow you to disable the new wrapper (which caused the low FPS in my case). Play around with the settings. You'll see the new wrapper is disabled when the DS application switches desktop resolutions when running.
The new wrapper runs the game in the full current desktop resolution and scales, which causes slowdown on some (older) machines.

What settings exactly, @TomKuurstra? I am having trouble getting over 19fps with a machine that should definitely be able to handle it. I did get a resolution change for the menu, not sure if it changes back when in game.

A curious thing too is that the menu loads up with 400+ fps and then goes down to 55ish. Not even 60.

Disabling Vertical Synchronization in dxcfg file (located in Dungeon siege game folder) fixed low fps for me.

It seems the engine has its own way of doing VSync/FPS cap. I've always found that quite bothersome as it can get in the way of wrappers or simply a smooth experience.

Here are some command arguments you can try in addition to the above tips. Add them at the end of the Target field in the game's shortcut properties / Galaxy's command argument field / etc.

vsync=true / false
bltonly=true / false
asynccursor=true / false (can help if the cursor is laggy)
maxfps= [number] (more reliable than external FPS cap?)
fullscreen=true / false

That's really strange. After disabling v sync i was able to get stable 60 FPS , on a laptop with just integrated graphics. You might try disabling Antialiasing and anisotropic filtering (in dxcfg file) , maybe it will help. Other than that i have no idea what could cause such fps drops.

Probably any DX wrappers will cause performance loss.

I'm running Steam-version with a DGVoodoo wrapper (to not get any mouse flicker or any weird graphical issues like crashes, freezes, etc)...and I'm lucky if I can do 30-40fps with V-Sync off & shadows on simple here on one of my gaming laptops (Acer Nitro - i7 4720 HQ, 16 GB RAM, 4gb GTX 960m, W10 x64).

Since this game's old, I doubt it was optimized for multiple core CPU's, more than 4GB of RAM (this game was released during XP era of Windows), and/or things of that sort.

Has anyone thought of using one of those Large Address Awareness programs to modify the EXE and see if we get better performance with it noticing you have more RAM and actually having more than 4GB of RAM installed?

EDIT:
I'll have to try that, when I get home - see if using a LAA program can improve performance for this game.

Indeed default GOG's DX wrapper is responsible for dramatic FPS drop in this game. Deleting "ddraw.dll" from game folder helped to fix this. Moreover, changing wrapper to DGVoodoo helped as well, especially in getting from 1024x768 frame, although picture can be stretched if non-4:3 is chosen.

I suggest author to choose mr. Marty1's answer as a solution for this topic.

To me, with a terrible computer, the wrapper run too slow and I prefer run it with the ddraw.dll renamed.
But as a note, without the use of the wrapper some users could encounter that the game crashes when loading a game with an error about "1024x768 16 bits not suported" or something like that. In that case using the command line bpp=32 should solve the problem; selecting a 32 bit resolution into the game apparently is not enough.

In any way I have noticed that disabling vsync from the wrapper, and/or letting app use the resolution, not desktop, use to make the framerate smoother in each GOG game that uses this dx 1-7 wrapper.

All of this just testing the GOG game without Legends of Aranna Installed.

I remembered about an option in DS! and DSII.
In game configuration there is an option about "application priority" regarding to the cpu power the game uses. It use to be disabled by default. If enabled the framerate improving should be noticeable even with the wrapper enabled.

greetings.