Your hardware seems fine to play the game on. Your drivers are probably outdated, but my current feeling is that the pending end turn issue you are describing is probably linked to optimizations that are still needed.

The lag when opening a window is very odd, do you mean it happens whenever you open menus and everything?

Thank you for the Answer so far! I will try to update the Drivers but i thought they are ok because i just installed a new Windows Version 64 bit to play the Game (have 32 bit so far). ;) 

The Lag is almost everytime when i go into a new Screen like Diplomacy, Technology, Hero and so on and when i go in the System Building Screen. But i see i wrote "several minutes". Thats not right. Not minutes but many Seconds  up to a Minute maximum Lags.For Example the Hero Screen is very Bad going to it...Lag...then go to the Upgrade Ability Screen...Lag... so there are two Times i can make a Tea just to Upgrade a Hero ;)

Can't tell how much RAM you have from what you posted, but Windows 32 bits versions have a hard cap on 4GB of RAM, usually more than Endless Space 2 would need. New installs of Windows don,t necessarily include new drivers, quite the opposite.

Go to AMD's website and find which ones are right for your pc:
http://support.amd.com/en-us/download

Hey i just want to say that the Game works better than ever now. Ok i upgraded my Pc slightly and buy a SSD Card what was good i think but all other Performance Improvement comes definitivly from the Patches and the Upgrade of the Game. Thank you so much!

Glad to hear this rettim77!

Closing the thread now