Quote: "I would like to ask, in rough terms, how complex would it be to migrate a DGDK 1.0 project to DGDK 2.0"
Getting a project up and running with DarkGDK 2.0 is very easy to do. The difficulty you will experience in the transition will be from some renamed functions, reordered parameters, and obsolete commands.
For example, DarkGDK 2.0 does not include the file handling library; you must use the commands provided by the host language.
Quote: "Also, how does DGDK 2.0 performs? Is it equally fast to DGDK?"
From what I've seen on a function-for-function basis it is faster than DarkGDK 1.0 but slightly slower than DBP due to some overhead. However, you gain the ability of being able to use a more powerful language with it such as C++.
Also, using DarkGDK 2.0 with DBP plugins is a snap. Most popular plugins are supported out-of-the-box.