I just got this game and was nonplussed to find that the full game had a significantly choppier performance than the demo. I've since learned a solution, but I wasn't able to find it scanning the gog archives so just in case it's not already here:
Open Settings.cfg with Notepad and add this line:
WAITRETRACE : 0
Then save.
As far as I can tell, it turns vsync off and gives a significant performance improvement at the cost of occasional texture overlapping.

There is a whole thread about performance tweaks, one of them that I figured out is to enable 32 bit color dept with sacred-config, and then disable the gog default shortcut compatibility for running in basic color depth.

After trying both the solutions provided in the readme and the fiddling with nVidia, the most effective on my machine, running win7, sadly seems to be to just zoom into the middle view when in a town with heavy traffic. I've tried loads of combinations of tweaking nVidia and Sacred (also through the Settings.cfg) but sadly to no avail.
I've also tried different settings of compatibility via windows. The 98/ME setting seems to run a tad better but the mousepointer begins to lag horribly. Otherwise choosing a different compatibility setting doesn't seem to help.
Lowering graphics detail ingame via options to medium helps a bit too though, cranking it all down to low helps quite a bit, but eliminates all farmers and citizens from the game...
PS: I've stumbled upon another forum where someone mentioned the possibility of DirectX10 messing with fps... But I know nothing about technical stuff like that.
PPS: I actually managed to find someone who reported Sacred to work fine with win7, though he doesn't explain how:
http://www.bleepingcomputer.com/forums/topic277294.html
EDIT: I've finally found a somewhat tollerable and working setting... Very similar to carlos' tip, though it didn't work for me first time for some reason - must've done something wrong:)
Here goes:
1st Open [SacredGold] Settings, have everything checked other than Video Compatibility Mode (I left Create Program Log File unchecked as well).
2nd Open nVidia Controle Panel:
Anisotropic filtering: 8x (seemed to be no difference between 2x, 4x and 8x)
Anisotropic test optimization: on
AA [Anti-Aliasing] gamma correction: on
AA transparency: off
AA: 8x (seemed to be no difference between 2x, 4x and 8x)
AA mode: improve program settings (override turns the screen to a "chess board")
VSync: forced on
Triple buffering: on
Merge optimization: off (turns off multiple cpu use)
3linear optimization: on
Negative LOD-bias: hold
Mipmaps: off
Finally, it still seems necessary to zoom to middle view when in populated areas, but at least the game now runs a little closer to smooth when in the wilds.

Disabling VSync gave me a decent FPS boost. I added the WAITRETRACE line to Settings.cfg, and I also forced VSync off in NVidia's control panel, just to make sure.
I should also point out that I'm playing this game on a netbook (Asus N10J), with a 1.6GHz Atom and a GeForce 9300M GS. On this rig, the CPU seems to be the bottleneck for Sacred (and many other games) : overclocking it a bit improved the framerate.
Previously I was stuck at 30 FPS, with occasionnal drops at 20 (middle zoom level). Now I have fluctuating FPS, between 25 and 40. Reducing the texture filtering in NVidia's control panel also helped a bit, but this has a significant impact on visuals. Overall, I have reached a fairly playable framerate at middle zoom level. Zooming out is not an option on this rig, though.

Have ou tried Windows Mode ?
Worth a shot at least

Thanks for the tip, I'll give it a try. However, even if windowed mode improves my framerate, I'm not sure it'll be comfortable on this machine. The screen resolution is only 1024*600, so I already have to downscale the image to get the fixed resolution of the game, which is 1024*768, to fit on the screen. NVidia's drivers do a great job here : I've tried to deactivate the scaling (in this case, I can only see a fraction of the picture) and the framerate is exactly the same, so the downscaling does not seem to impact framerate.
Therefore, if I run the game in windowed mode, I'm not sure I'll be able to see the whole game window on my little screen, but it's worth a try.
Anyway, I consider that 30-40FPS is fairly playable for an action RPG. Besides, on such a small screen, the graphics look great, very sharp and not aliased at all, which makes up for the occasional slowdowns.

I' ve found a solution!

Sacred has problem with more then one CPU.

When Sacred is running, just open task manager and set only one CPU for Sacred and voila runs smoothly.

see image: http://imgur.com/a/0PDYn

I'm a moron. How exactly do you do that?
I know how to open Task Manager, but where do I go from there?

Do I have to restart the turned off CPU when I'm done playing?

Wait, I think I see it.

Didn't work. :-(

Hi,

fps dropping at zoom out in villages. (ca. 15fps)
after hours of searching and testing....
and all other fixes are not working...


i used the "High-resolution rendering tool" as discribed here:

pcgamingwiki.com/wiki/Sacred

i used at the dgVoodoo 2 site the version 2.53.
copy the 3 dll files from the ms directory and the dgVoodooSetup.exe file, direct in the sacred folder.
start the dgVoodooSetup.exe, push the ./ button on the first tab. the sacred.exe should appear in the file path field.
after that, set on the 3-tab your resoltion in the drop down field (e.g. 1920x1080)
uncheck watermark button and apply.
close dg voodoo.
run sacred without fps drop.

in the sacred config.exe, i only checked fullscreen and 32bit

hope it helped

it fixed for me when I went to Win10. Don't even ask me why. :P