Hey Jeroen,
If you are going down the ccTLD route I would host each sites it's respected country, it's possible Google will apply some weight to the geo location of the IP address (you should also set the location in WMT).
But more importantly hosting in the same country is going to improve site load times which will help out (a tiny bit atm) with google and improve the user experience.
Hosting in another country is not going to get you "penalised" by Google but it's not going to send a signal (from the geo location of the IP address) that you are located in Germany - this may or may not affect your rankings.
I recommend you watch this video: http://www.seomoz.org/blog/international-seo-where-to-host-and-how-to-target-whiteboard-friday
Hope that helps...
Keith