Gentlemen.

I found a solution to most performance and low framerate issues with Jagged Alliance 2.

I am running JA2 Gold 1.13 v4870. I was getting extremely low framerate and lags, a single bullet would fly for like 5-10 seconds. Then I remembered a solution to a very similar problem in Planescape: Torment.

The solution:
...is to make JA2 engine run on WineD3D instead of regular DirectX. WineD3D is a component of Wine and is generally used to run Windows apps on non-Win systems, but can also be used on Windows.

How to do that:
1) Download wined3d.exe from http://www.nongnu.org/wined3d/
2) Don't run the program! instead, extract it's contents with 7Zip or somesuch http://www.7-zip.org/download.html
3) Copy ddraw.dll, libwine.dll and wined3d.dll from extracted $SYSWIN folder into the root folder of your JA2 installation (e.g. C:\Games\Jagged Alliance 2 Gold\)
4) Run the game. It may take a bit longer to start
5) Enjoy one of the best games ever in as high FPS as your hardware can handle

Credits:
- Guys who made WineD3D
- aqrit on Spellhold Studios board for the Planescape: Torment FPS solution, of which this is a shameless duplicate

This may work with other oldies as well. Use at your own risk.

Cheers,
phoenicksCZ