[eluser]Seppo[/eluser]
Are you talking about creating something like "Mysql_old_driver" (you can use a better name =P) ? I like that idea... although you will be having 3 drivers using a mysql server where you should change each thing... (OK, I'm reading "Refactoring" by Martin Fowler and it really got me against duplicated code!)
I like the idea of the config file because you can update easily and I don't think it is an exception - You are setting the config to not use it.
And about the overhead... I think many things can be done to improve performance - For example a way to avoid hooks / benchmark classes to be loaded that most of the time are not used and yet loaded on every call. (I've been thinking that for a while and now I have the opportunity of writing it =))
