Latency issues on local development server
In the end I resolved my problem - which was unfortunately not related to craft at all. For unknown reasons there it was just quite evident visible. 

Facts:
I'm running MAMP on a local OSX (Yosemite) setup. My craft website is running on a virtual domain pointing to localhost. 
PHP 5.4
Mysql 5.x
Craft 2.3.26 Pro version

Issue:
Long latency (~10s) when editing an entry/adding stuff.

Solution:
In the end it was related to OSX issues with resolving a vhost address and resulting in loopbacks. A detailed description of the issue und how to resolve it can be found on stackoverflow.