Yes blueprints are fast and nice. So no performance problems at all.
But they have other aspect that limits scope of projects created in them.
You see as graphical programming script, any code done in blueprints takes up several screens, sometimes i feel that my whole code done in blueprints that takes 10 or more screens would fit in 100 or so lines of C++ * that is around single screen).
So when your project grows you are losing track of code much faster than with projects done in C++. At some point you want to change something in old code, it is much faster to find it in C++ than find which blueprint it was in.