I can do my turns fast enough, its the computer thats getting on my nerves
I know what you're talking about. The game tends to lag as the cache augments. The trick is really simple and costless in energy if you have a screen sufficiently big. Make your games under window mode and when it lags, change the window size. Takes less than a minute and refresh the game just like it was restarted. No need to restart and wait the initialization (and thus extremely useful when playing mods under SVN as the init can take up to 20 mins occasionally).
Is there an alternative to that? I really prefer Fullscreen in Singleplayer.
Simply alt-tabbing seems to solve the memory leak issue.
Windows Task Manager (Ctrl + Alt + Del -> Task Manager)