I don't own the game (debating buying), but am wondering if this helps people with performance issues. Taken from the developers forum:
Re: Game running slowly, and low FPS
Postby FocusTechSupport » 25 March 2013, 10:30
Please modify the graphics configuration file in order to improve the game perfomances:
1. Open the folder Cities XL Platinum located on the hard disk.
2. By default the game is installed in the Local Disk (C:), Program Files or Program Files (x86) and Focus Home Interactive.
3. For the Steam version, the path is the Local Disk (C:), Program Files or Program Files (x86), Steam, SteamApps then Common.
4. Open the folder Data then the folder Config.
5. Right click the file GlobalSettings.cfg and click Edit or open the file using the Notepad.
6. Go to the line Live and set PoolSize to 4096 => <PoolSize>4096</PoolSize>
7. Go to the line Layout and set ProcessEnabled to 0 => <ProcessEnabled>0</ProcessEnabled>
8. Go to the line Visibility Manager and set VisibilityEnabled to 1 => <VisibilityEnabled>1</VisibilityEnabled>
9. Save the file GlobalSettings.cfg and run the game.
As soon as you experience major slowdowns with your city, please save your city then quit the game (go back to the main menu) and reload your city.