Class.forName will cause the class to be loaded (if it is not already). You do not have to use newInstance if it is only going to create an instance you're never going to use. If you do use, all good.
If you tell the difference between Cllass.forName() and loading the class directly I'd be very surprised, and since it only occurs once for the life of the application it really shouldn't have any impact on performance except at the moment they're all loaded.
*If* you have a fixed set of classes, you could put Abstract Factories into a Set, with the classnames as keys.
But I doubt that the performance difference is significant. I would only try it if the other way *proved* to be too slow.
The soul is dyed the color of its thoughts. Think only on those things that are in line with your principles and can bear the light of day. The content of your character is your choice. Day by day, what you do is who you become. Your integrity is your destiny - it is the light that guides your way. - Heraclitus