So, I was messing with the games files a bit and I found out that making the log file read only prevents the game from stuttering.

And then I tinkered with the EngineSettings.xml file in the game's folder, there's a value called <DefaultGameSpeedForSkirmish> that you can edit, I've set it to 20 (default is 40) and it's now running at a decent speed.

Hope it helps !

EDIT: (Removed blabbering about he first game.)

Thank you for the tip on stuttering.

I don't play multiplayer on this game so no idea if it works for that too... The only other parameter that I found so far is about campaign mode, there's also a notion of speed for some maps but I didn't try to mess with thoses.

Ooops! I missed this being about C2... which I have not played, terribly sorry.

It works well. Many thanks